I had a similar issue on one of my HS300s in January.
The issue happened several more times on that HS300. Sometimes I rebooted Sense to regain performance, and other times I found that waiting 24 hours solved it. Last week I “retired” that HS300 since I was no longer using it much anyway. I assume something was going bad in that hardware, as my other HS300 never gives me issues, and neither had this one previously.
I hope you find a better solution than mine!