rb433ah firmware/ros problem..

Hello,
im having some issues with 4xrb433ah.
after the 6.25 ros and the 3.23 (im not sure cause they stuck now and i cannot reset them to check) the rbs are running with 100mhz cpu, they stuck every day or 2 days is the uptime score… and i cannot upgrade them without netinstall.
I have changed the capasitors, power supplies and the wifi cards but the problem still remains…

q1. is there any way to downgrade the firmware??
q2. have you seen this problem again? and if yes what was the solution?

*info. my wifi cards are atheros cm6/cm9.

Thank you.