I have an Arquitens that falls off the clear plastic stand if touched.

I compared it to my other Arquitens, and the ship looks fine. The clear plastic stand seems to be too short by about 2mm.

Did anyone else run into this? If so, how did you fix it?

Super glue

I'd say take the transparent keyhole off, it is sometime badly glued, and has no real use whatsoever (I took off all mine that could be taken without breaking anything)

or if you think the keyhole is faulty, ask for a replacement from FFG, you may get one free if you can give a photo proving it

I took it into the FLGS where I purchased it. He offered to swap it out if he couldn't "fix" it.

I agreed, so he took a scalpel and removed some of the plastic from the top and front of the plastic stand, so that it was level and square.

He then put a few drops of plastic glue on the sides of the plastic stand let them dry.

Afterwards, the plastic stand worked fine.

If viewed from the side, you can now see that the stand is now more than 2mm too short, but the ship stays on the stand properly.

I think my MC30 is also doesn't fit snugly, so I will try the same trick with the glue.