When i have polling issues.. I'll do a repair of the Job Engine.. I'm not sure if that exactly fixes but to do the repair you stop and restart services which might also be fixing the issue.
Here's the link to the how to..
If you're not comfortable doing this please reach out to Solarwinds Support and they should be help you do it and/or find the actual issue.
I also have seen polling issues when the device you're polling has memory and/or cpu issues as it might be drop SNMP request due to load.
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