Sounds like you've eliminated a number of possibilities.
What type of contactor or contactors are being used? The late 1990's Futuras used a pair of loop contactors with huge micro switches under the coil. Problematic design. Faults 18 & 94 you get about every time a recovery has initiated.
Does this job use the RVU Wizard thing? If so, you can set the system to capture just about any fault then playback the screen and watch all inputs before the fault occurred... great tool. Are the ropes sliding on the sheaves maybe?
And lastly, has the building put any antennae or satellite dishes and their associated cabling near the machine room? Ask me how I know about this one! No wait...don't!