My B above middle C is sticky. Making me nuts! Not sure how to proceed / troubleshoot / repair… Thanks!
Replying to my own post. Took key out and saw zero issues with it (no cracks, burrs, dirt, blah blah). I cleaned it and re-assembled. Now working as expected. No idea what the issue was.
I did notice quite a bit of lube. Factory installed I am sure since I am original owner and case has never been cracked.
Oh yeah, Yamaha tech support was all “too bad so sad”, buy a Roland next time…
Be mindful of any debris that might have been dislodged when you took the key out. Tiniest bits can affect the velocity sensors. Other future option are to swap that C key with another,
Check if the B or C key is leaning to the left and touching the key next to it. When pressed down, the keys will jam and one stays down. Attributed to a bad run of plastic, but you will not see anything wrong with it by pulling it out and inspecting. Replace the leaning key is the only fix if thats the issue.
Thanks so much for the helpful suggestions! The key is still working as expected. I play it about 60 minutes each day and so far so good 
Didn’t see any debris when I pulled the key. Actually the key bed was very clean.
The key does not appear to be leaning. That said, until I find the cause I would imagine it will reoccur and when I does, I now have some great ideas on what to look for and will update the thread.
Thanks again!!