Smooth PEI Sheet Delaminated on First Print  

Smooth PEI Sheet Delaminated on First Print

Hey folks.  So I ordered a new smooth PEI sheet from Amazon on Saturday (because I could get it on Sunday, rather than waiting to ship from Prusa to Texas).  There's a project I'm going to print for the wife, so I was working on a sample with some settings changes.  First couple of tries weren't working out after an hour or so, but the third one ran just fine.  It was a 40-hour or so job, a section of a helmet.  It was done when I came home from work today, so I lifted the bed sheet off, then flexed the steel to free the print.  The non-support area of the print partially delaminated the PEI from the sheet.  See the pic; text continues below.

That bubbled region is actually proud (sticks up); you can feel it quite prominently if you run your hand over it. I don't consider myself a 3d printing expert, but I have been using this printer for 5 years so I've got some experience.  This print was done with Hatchbox PLA, which I've probably used 20-30 spools of; and with the temperature settings I've learned work for me (200 nozzle/60 bed).  I've NEVER seen PLA do this to one of these sheets; also, I've used this spool before without issue.  (I have seen PETG do this--though not nearly to this degree--early in my printing learning, when I didn't use enough glue stick.)

So my questions for the group are: 1) Is this a defective sheet or is there another explanation? 2) Is there a way to recover the sheet (without replacing the PEI) or should I just look at returning it?