Hi.
My config: 2011UiAS (6.44.3) + Windows 2003 Small Business Server (with Active Directory)...
When I try to use pptp connection I got:
14:39:43 radius,debug new request 1b:02 code=Access-Request service=ppp called-id=ROUTEREXTERNALIP
14:39:43 radius,debug no radius server found for 1b:02
14:39:43 radius,debug timeout for 1b:02

I have this config:
/radius add address=MYADSERVERIP called-id=ROUTEREXTERNALIP domain=MYADDOMAIN secret=SeCrET5242 service=ppp src-address=ROUTERINTERNALIP timeout=2s500ms
/ppp profile add change-tcp-mss=yes dns-server=MYDNSSERVERIP local-address=ROUTERINTERNALIP name=vpn remote-address=vpn-pool
/ppp aaa set accounting=no use-radius=yes

Not working now. Is this feature or bug?

Your radius server is not found... start there. Your firewall is probably blocking somewhere.

I have it setup with no issues on both ppp and wireless for radius accounting with win AD+domain.

If radius server found it would look something like this in radius, debug, packet:
new request 1b:00 code=Accounting-Request service=ppp called-id=external-ip domain=your-domain
sending 1b:00 to radius-server-ip:1813
sending Accounting-Request with id 186 to radius-server-ip:1813
...

I used packet sniffer on MikroTik on internal bridge and did'n found any packets from MikroTik to RADIUS server... As you can see in the log there is no 3 sec (now I use 3 seconds timeout) between all debug messages !

SOLVED:
I removed "domain" from RADIUS server config page on MikroTik. Now I can see packets from MikroTik to RADIUS server.

Same! I removed the domain entry (xy.local) then Radius can auth and working fine. Windows 2016 server and CCR 1009 with 6.49.3