Hello everyone,
I already raised a ticket at support but would also like to see if anyone has also a clue what could be wrong:

I am currently migrating from virtualized OPNsense to virtualized x86 ROS.
So far the setup works pretty well but I am struggeling a lot with VRRP.
In general I have several VLANs at my network for which I would like to have a VRRP address to act as a gateway.
I created a master VRRP for my 1st VLAN and added the other VRRPs to the other VLANs + added group master to my 1st VRRP.
If every VRRP interface on router 1 has master status all other VLANs/VRRPs beside number 1 are working as expected and do have good internet connectivity.
Only for VRRP 1 the internet connection is far to slow - it takes around 20 - 30 seconds to open a site with just static content; on other VLANs the site is being opened within seconds.
Also I recognized if I reboot the router only the group master VRRP will become master while the other VRRPs stick at backup until I disable an reenable them.
My general setup is:
VLAN with a dedicated router os (192.168.10.170/24 on VLAN 10) + VRRP on VLAN with vIP 192.168.10.254/32

My network setup would be: WAN --> CCR2004 (as internet border router + BGP) --> 2x x86 Mikrotik --> several VLANs.

I'd take a look at this thread: viewtopic.php?p=972296#p972296
It has some details on the VRRP inner workings. You may want to use a group for all your VLAN's VRRP interfaces, so they all fall over at same time – then you have one active router, vs potentially some VLAN being on one router and some another.

But I'm not sure VRRP is related to why one VLAN be that much slow vs another... Something else is going on.

Thanks for the information.
In general I am using the group master feature, sync connection state and preemption mode on master.
Additional I am also using a script which adds OSPF costs to 65000 on the backup node so all traffic would be routed via the master router to my main internet router.

Without knowing the topology, but one thought is If you used the VRRP address of each VLAN in OSPF you may not need a script.

e.g. by using VRRP your trying make two routers look as one to the rest network,so IMO that including the upstream routing. So mixing OSPF into VRRP, it starts to get confusing...

It seems I had some misconfiguration/understood the settings wrong.
I only set all other VRRP interfaces to the master but I did not configure the master to be itself group master.
With this setting it works far better.

And I also unticked the "Preemption Mode" setting. So now from a network perspecitve it looks great and also my interface gets full speed.