i think i know what you mean andrew, (might be wrong) 😀
i think its because the tape is fixed firm to a solid panel but the face is sticking/holding the vinyl which is holding the acrylic.
when the acrylic expands and contracts lightly with heat/sun etc the tape stays strong in situ and as a result the vinyl is prized away from the panel where the tape grips?
as i said, may have picked you up wrong… however, i did a sign a good while back, i had similar issues, but not the same, end event was i had to us a small 10mm trim and slide the panel into it. or was it L-shaped trim around the edge? hmm cant remember sorry… anyway, just thinking out loud here, hope this helps… ….. a bit 😕 😕