Internal: MTX+3 losing config when powered down
The most likely issue is the config card battery backup is either run down and needs to be replaced (especially if the frame is 5 years or older) or the jumper associated with the config card battery is disconnected. Attached is a pdf of the config card layout, you should be able to pick out the battery and jumper quite easily.
With the Com 72 or SYS 200 frames, pull the config card and note the position of the jumper (clearly marked on pcb) or measure the battery voltage with a DVM.
The micro-matrix (24 port frame) is a bit harder to access the config card, the front panel of the frame has to be removed to access the config card.