This is quite odd - for me - in that I have been printing on my UM3 for several years (about 4 - maybe 5? time flies) - and I just this week started seeing this.
I have printed maybe 90% PLA over this time, I have printed only one full spool of CPE about 2 years ago. I have printed maybe a half spool of ABS and about three weeks ago started printing PETG for the first time. After my 2nd full spool of PETG, I got significant glass delamination (tagging for searchers: glass peeling, cracking, chipping, separating)
I use hairspray exclusively and always have. I have finished my PETG project for now and an currently printing PLA again. I offer you no help, only solidarity. Hopefully someone picks up on his thread and offers a cause / solution. (It is the cause that has e baffled.)