Second, because I'd dropped a board during build which dented a corner and bent one of the join clips.

This time though the damage is a little more terminal to the recently attached barriers:

Occurred during disassembly this morning when I wasn't being quite cautious enough to ensure that the board was properly supported during leg removal. Proves that the acrylic is pretty fragile, and acts as a reminder to me to be careful in all respects when assembling or disassembling the layout. I'll have to order replacements as repair would be impractical. I might make that a slight over order so as to have some spares in case of similar happening again.