You are correct, the line was missing, probably due to me deleting and recreating the snmp user as part of my troubleshooting. We have 2 VSX clusters that this happened on, and the line was still there on the other cluster.
Anyway, when I put the line
set snmp usm user ***** vsid 0-13
I get the message:
NMSSNM9999 Timeout waiting for response from database server.
And when I check the config, I see the line as:
set snmp usm user ***** vsid 0-4
If I run the command again, I get the same error but then the config says vsid 0-9. And I'm still unable to connect from the Solarwinds server.