I am having a similar problem. I was using The dude v4.0beta3 and I had some problems with "invalid OiD" in most of the SNMP communications even getting all the information I need throw SNMP Walk. So I decided to test the v3.6 of The Dude and it is now working fine for most of the devices but, in RoS v5.x I can't see the RouterOS version or event Interfaces under RouterOS tab of the device (throw SNMP I can read everything now).
Just to ilustrate I am sending this image:
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Is there anything I can do besides upgrade Dude?