Unstable Custom 22 neck

[Phoenix 5]

I bought a used 98’ Custom 22 about 3yrs ago. I’ve been having problems with neck stability. I keep the neck as straight as possible and it tends to shift often, being too convex. I have other guitars set up the same way with no problem. I’m finding it hard to like my PRS. What shall I do to solve this issue?

 

[Psydoc]

Send it to PRS.

 

[Phoenix 5]

Send it to PRS.

I currently have the guitar set up with 9’s. I’m thinking of putting 11’s to see if that helps with the instability. If nothing changes, I’ll see if PRS can help me out.