The TV controls are separate from the other controls (unless you set up the remote for CEC control of the TV), so it's possible for the TV controls to work and the others to not work. It's likely that the remote is losing its connection to the stick, but what's causing this I couldn't say. Have you tried pairing the remote to the stick again?
How to set up your Roku® voice remote | Official Roku Support
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee.