Setting The Dude 6.48.3 and same devices are not properly responding do SNMP
The main problem is on the picture. Same source device, same target.
Same Dude server but once it is connected via public IP 194.x.y.z and the second is vi VPN.
Removing, adding … reprobing … same problem
Server on 1100AHx4Dude, Probed device is RB 4011iGS+ but other non 4011 device behave same way.

have you added smtp v3 profile on smtp profiles (no present on default)
and set it as smtp v3 profile on device properties,
and also set smtp v3 inside RouterOS?
Of course I did. The log is from the same device monitored from one Dude server
Lines 1,2,6,7,8 are log of communiction with Dude via public interface.
Lines 3,4,5 are log of “talk” made by “local” interface = VPN connection
One question, please
Why you would use v3 (can be a security risk) instead of using simply v2c?
From you reply, I can deduce you want use v3 (read/write) just because “last version, better version” reasoning.
Actually if you don’t need it (because you know what it is for), ALSO for security reasons, better use the v2c (readonly) which also uses less resources on the machine
No matter what, the problem still exists: what is the cause of “unknown engine id”?
You have asked that to the support?
Asking forum users . Maybe it’s trivial misconfiguration and there is no sense to open ticket.
Thanks for do that.
But I do not remember similar errors also on other user posts. :((
I’m on forum from 2014, can’t remember 2012 :))
and also I can not remember all from 2014 to now :)))
I suggest you to contact MikroTik if you do not have already do.
Thanks.