I upgraded to Cirrus v4, imported my nodes from Access, deleted them and re-imported them after creating my custom properties. Now most of them show "No SNMP Support". They poll fine and I can go to the MIBs button and get System Info and other tables.
I've turned polling off and then, after waiting a day, turned it back on. It's been on for a couple of days now and all my devices are still "No SNMP Support". Cirrus has been restarted several times. When I select a node group and attempt an Inventory I've found a few devices that work but mostly it just comes up with an empty box that closes after a few seconds.
I had a very similar issue in 3.5.1 with no real fix. I'd turn monitoring on/off and restart Cirrus and eventually the stars would align and my device would develop SNMP support. Is there a bit I can flip in the DB to turn this on?
Edit: Out of 596 devices I'd guess about 100 show SNMP support. All of them worked on 3.5.1.