Is there any chance you're using a Netflix account of a friend/family member that doesn't live in your home? Netflix has already announced they were cracking down on people sharing a single account. They might be starting enforcement on Roku devices, before they move on to others.
If that's not the case, then the first suggestion is to remove the Netflix channel from your Roku, reboot the Roku (do not skip this step), then after the reboot install the channel again. Sometimes apps get corrupted and a remove/reboot/install clears the bad code. If you don't reboot it, the removal is never completed and the corrupt code could remain in memory.
Dan
Roku Community Streaming Expert
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