If you are using the proper fill and bleed procedures and are still seeing collapsed hoses, the likely suspect is the cap vacuum relief valve. Could be that just the act of removing and installing it causes a malfunction on the next several cycles, and then it works properly again until the next time you remove it.

You might also want to check that the vent line from the top of the themostat housing to the supply tank is not clogged. Try removing it at the expansion tank (and remove the tank cap too) and see if you can blow through it. There will be some resistance, but the coolant in the system will be able to expand into the tank.

Get the cap tested for for both pressure or vacuum relief operation, or just buy a new one and see what happens.

Duke