Couple ides:

Y harness is failing. Thats why I don't use them in large planes. Plug each servo into it's own port and mix them with the TX or use a JR Matchbox.

The servos are fighting each other. Your running 2 very high precision servos on a single aileron with a Y harness to tie them both together. The linkages might not be perfect, or a control horn is a little off. The servos are fighting each other. Use a Matchbox or the TX to mix them.

Pots in the servos are starting to get bad. Seams funny that they would both fail at the same time. I've never even had a JR servo go bad. Been using and abusing them for yrs and have never had one go bad or need servicing.