I found out what my problem was! My CH Fighterstick was losing the x-direction pot. The condition finally got bad enough that I replaced it with my backup Fighterstick. I will add that roll rate and control has increased significantly with the new stick!
I'll either order another pot from CH Products and replace it myself or send the whole stick back to them, depending on the cost. The y-axis (pitch) is just fine, which leads me to think it was a defective pot. So, if your stick is losing calibration it's likely the stick is going bad.
Regards,
Malta