May be this has nothing in common with the clock bridge problem but, I discovered two weeks ago a tiny hole on the Sinclair200 Spectrum Emulator plate.
It affected one of the Eprom address lines, probably the original problem with the faulty chip. Do you remember?
I have heard something similar made on baggages at customs when returning from Colombia. Little holes made on all the content of the travel bag.
Please Zozo, check the tracks of Szôrg bridge for millimetric drill holes.