Hi NetWorker,
I checked with a PC through USB Tethering and the speeds were excellent so I doubt that it has to do with cell congestion, I am also leaning towards a misconfigured USB driver in the Mikrotik router. I am posting a copy of the config below. When running through android 4G, I disable the cable connection dhcp client and change the masqurade to use LTE1
# mar/21/2019 12:20:57 by RouterOS 6.44.1
# software id = RLY1-NJ03
#
# model = RB750Gr3
# serial number =
/interface bridge
add admin-mac=B8:69:XX:XX:XX:XX auto-mac=no comment=LAN1 name=bridge1
add admin-mac=B8:69:XX:XX:XX:XX auto-mac=no comment=LAN2 name=bridge2
/interface lte
set [ find ] mac-address=DA:92:XX:XX:XX:XX name=lte1
/interface ethernet
set [ find default-name=ether1 ] comment="ABB WAN"
set [ find default-name=ether2 ] comment=BR1
set [ find default-name=ether3 ] comment=BR1
set [ find default-name=ether4 ] comment=BR2
set [ find default-name=ether5 ] comment=BR2
/interface list
add name=WAN
add name=LAN
/interface wireless security-profiles
set [ find default=yes ] supplicant-identity=MikroTik
/ip hotspot profile
set [ find default=yes ] html-directory=flash/hotspot
/ip pool
add name=dhcp ranges=192.168.0.2-192.168.0.254
add name=ovpn-pool ranges=192.168.8.2-192.168.8.99
add name=l2tp-pool ranges=192.168.9.2-192.168.9.99
add name=vpn ranges=192.168.89.2-192.168.89.255
/ip dhcp-server
add address-pool=dhcp disabled=no interface=bridge1 name="DHCP LAN1"
/ppp profile
add dns-server=8.8.8.8,8.8.4.4 local-address=192.168.8.1 name=ovpn-profile remote-address=ovpn-pool use-encryption=yes
add dns-server=8.8.8.8 local-address=192.168.9.1 name=l2tp-profile remote-address=l2tp-pool wins-server=8.8.4.4
set *FFFFFFFE local-address=192.168.89.1 remote-address=vpn
/interface bridge port
add bridge=bridge1 comment=BR1 interface=ether2
add bridge=bridge1 comment=BR1 interface=ether3
add bridge=bridge2 comment=BR2 interface=ether4
add bridge=bridge2 comment=BR2 interface=ether5
/ip neighbor discovery-settings
set discover-interface-list=LAN
/interface detect-internet
set detect-interface-list=all
/interface l2tp-server server
set default-profile=l2tp-profile enabled=yes use-ipsec=yes
/interface list member
add comment=LAN1 interface=bridge1 list=LAN
add comment="ABB WAN" disabled=yes interface=ether1 list=WAN
add comment=LAN2 disabled=yes interface=bridge2 list=LAN
add comment=WAN2 interface=lte1 list=WAN
/interface ovpn-server server
set auth=sha1 certificate=server-certificate cipher=aes128,aes256 default-profile=ovpn-profile enabled=yes require-client-certificate=yes
/interface pptp-server server
set enabled=yes
/interface sstp-server server
set default-profile=default-encryption enabled=yes
/ip address
add address=192.168.0.1/24 comment=LAN1 interface=ether2 network=192.168.0.0
/ip arp
add address=192.168.0.5 comment=SERVER interface=bridge1 mac-address=70:8B:XX:XX:XX:XX
add address=192.168.0.6 comment=HTPC-LR interface=bridge1 mac-address=BC:5F:XX:XX:XX:XX
/ip cloud
set ddns-enabled=yes
/ip dhcp-client
add comment="ABB WAN" dhcp-options=hostname,clientid interface=ether1
/ip dhcp-server lease
add address=192.168.0.11 comment="SMA SOLAR INVERTER" mac-address=00:40:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.4 client-id=1:50:c7:XX:XX:XX:XX comment="TP-LINK AP (GF)" mac-address=50:C7:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.3 client-id=1:50:c7:XX:XX:XX:XX comment="TP-LINK AP (1STF)" mac-address=50:C7:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.12 client-id=1:0:5:XX:XX:XX:XX comment="DENON AMP" mac-address=00:05:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.9 client-id=1:24:5e:XX:XX:XX:XX comment="QNAP NAS" mac-address=24:5E:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.2 client-id=1:b0:4e:XX:XX:XX:XX comment="TP-LINK SWITCH" mac-address=B0:4E:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.16 client-id=1:cc:d3:XX:XX:XX:XX comment="MAXXTV (D/S)" mac-address=CC:D3:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.5 client-id=1:70:8b:XX:XX:XX:XX comment=SERVER mac-address=70:8B:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.6 client-id=1:bc:5f:XX:XX:XX:XX comment=HTPC-LR mac-address=BC:5F:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.8 client-id=1:3c:2a:XX:XX:XX:XX comment="BROTHER PRINTER" mac-address=3C:2A:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.13 client-id=1:f4:7b:XX:XX:XX:XX comment="SAMSUNG-TV" mac-address=F4:7B:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.14 client-id=1:e4:7c:XX:XX:XX:XX comment="SAMSUNG-TV" mac-address=E4:7C:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.15 client-id=1:cc:d3:XX:XX:XX:XX comment="MAXXTV (U/S)" mac-address=CC:D3:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.17 client-id=1:18:68:XX:XX:XX:XX comment="HIKVISION NVR" mac-address=18:68:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.19 client-id=1:b8:27:XX:XX:XX:XX comment="RPi [WIFI]" mac-address=B8:27:XX:XX:XX:XX server="DHCP LAN1"
add address=192.168.0.18 client-id=1:b8:27:XX:XX:XX:XX comment=RPi mac-address=B8:27:XX:XX:XX:XX server="DHCP LAN1"
/ip dhcp-server network
add address=192.168.0.0/24 comment=LAN1 gateway=192.168.0.1 netmask=24
/ip dns
set allow-remote-requests=yes
/ip dns static
add address=192.168.0.1 name=router.lan
/ip firewall filter
add action=accept chain=input comment="accept established, related, untracked" connection-state=established,related,untracked
add action=accept chain=input comment="accept OpenVPN" dst-port=1194 protocol=tcp
add action=accept chain=input comment="accept ROUTER (SSH)" dst-port=11122 protocol=tcp
add action=accept chain=input comment="accept ROUTER SSL" dst-port=11443 protocol=tcp
add action=accept chain=input comment="accept ROUTER WINBOX" dst-port=8291 protocol=tcp
add action=accept chain=input comment="accept ICMP" protocol=icmp
add action=accept chain=forward comment="accept IN IPSEC policy" ipsec-policy=in,ipsec
add action=accept chain=forward comment="accept OUT IPSEC policy" ipsec-policy=out,ipsec
add action=accept chain=input comment="accept IPsec NAT" dst-port=4500 protocol=udp
add action=accept chain=input comment="accept IKE" dst-port=500 protocol=udp
add action=accept chain=input comment="accept l2tp" dst-port=1701 protocol=udp
add action=drop chain=input comment="drop invalid" connection-state=invalid
add action=drop chain=input comment="drop all not coming from LAN" in-interface-list=!LAN
add action=fasttrack-connection chain=forward comment=fasttrack connection-state=established,related
add action=accept chain=forward comment="accept established, related, untracked" connection-state=established,related,untracked
add action=drop chain=forward comment="drop invalid" connection-state=invalid
add action=drop chain=forward comment="drop all from WAN not DSTNATed" connection-nat-state=!dstnat connection-state=new in-interface-list=WAN
/ip firewall nat
add action=masquerade chain=srcnat comment=masquerade disabled=yes ipsec-policy=out,none out-interface-list=WAN
add action=masquerade chain=srcnat comment=masquerade ipsec-policy=out,none out-interface=lte1
add action=masquerade chain=srcnat comment="masq. vpn traffic" src-address=192.168.89.0/24
/ip service
set telnet disabled=yes
set ftp disabled=yes
set www disabled=yes
set ssh port=11122
set www-ssl certificate=https-cert disabled=no port=11443
/ip smb
set comment=Mikrotik domain=WORKGROUP enabled=yes
/ip smb users
add name=admin read-only=no
/ip ssh
set allow-none-crypto=yes
/ip upnp
set enabled=yes
/ip upnp interfaces
add interface=bridge1 type=internal
add interface=ether1 type=external
/ipv6 address
add address=::ba69:XXXX:XXXX:XXXX eui-64=yes from-pool=abb interface=bridge1
/ipv6 dhcp-client
add add-default-route=yes interface=ether1 pool-name=abb pool-prefix-length=56 request=address,prefix
/ipv6 firewall address-list
add address=fe80::/16 list=allowed
add address=ff02::/16 comment=multicast list=allowed
add list=allowed
/ppp secret
add name=admin profile=ovpn-profile service=ovpn
add name=admin profile=l2tp-profile service=l2tp
add name=vpn
/system clock
set time-zone-name=Australia/Melbourne
/tool mac-server
set allowed-interface-list=LAN
/tool mac-server mac-winbox
set allowed-interface-list=LAN
Thanks.