P3D v.2.5.12945.0 Win 8.1
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Control settings (Saitek X-55) randomly refuse to be regognised and controls randomly default to (the useless) 'Mouse Yoke'. Surely there must be a simple 'cure'?
The easiest fix is to use the registered version of FSUIPC for all controller key and axes assignment.
Apart from that you can try to disable all USB power saving options, from time to time the controller is recognized then by the sim.
I found another tip on the internet, if you load the deep sea mission first after starting the sim the joystick is recognized and you can configure it. I tried it and it worked for me.