On Sat, 08 Sep 2018 or thereabouts, Michael came forth with:
Perhaps start by issuing the following command from your observium box (just break the output with a ctrl+c, otherwise it will continue for a very long time)
snmpwalk -v2c -c **** jr01 .1
Just use your community string where the **** is. The .1 will start the walk at the very top most index level in SNMP and won't need any MIBs to load correctly in order to function.
If the command succeeds, it will spew out possibly thousands of lines/results if you don't send a break to it.
If that command doesn't produce any meaningful results, then I would start working through the list I sent earlier.
Thanks Michael and Adam,
This is now solved.
I replaced the contents of /etc/snmp/snmpd.conf from my previous installation with the contents described here:
https://docs.observium.org/device_linux/
I can only assume (didn't do a diff) that there were some changes from what I used 2yrs ago (or so).
Many thanks.