Please help: Warping on the corners of my prints with Wham Bam flexible PEX bed

[curious aardvark]

the best print surface I've used is printbite, but cheap self adhesive PEI is a good alternative.

I also add the odd bit of print glue, for stubborn filaments: different filaments have very different sticking properties. So some generic print glue (not pva or hairspray) will just sort any issues.

As far as trusting the internet goes - use your noggin.
If a product is recommended by someone obviously being sponsored by the manufacturer - take the 'review' withn a large pinch of salt.
people like myself and gambo, who alas are not paid by anyone - will give you more unbiased advice based on personal experience.
Don't get me worng if anyone wants to send me free stuff - I'll definitely err on the side of positivety in any review :-)
But at the moment, I'm 4 for 4 with manufacturers promising to sedn me review printers and then no printer ever appearing.

And for the record - any review that states the product was given to the reviewer - has to be suspect.
Nobody wants to bite the hands that are feeding them.
Youtuber 3d print folk frequently say: 'we were not paid for this video'.
While also stating the printer was given to them for review. In my book that counts as payment.
So any review based on that relationship between reviewer and manufacturer, is suspect and can never be totally unbiased.

Evidence by all the glowing reviews of creality printers - versus the real world misery of many creality printer owners.

Any print surface that asks you to sand it before use - is just relying on the micro-pits you've just added to the plate to grip the filament. it's clearly not an actual chemical process.

A $10 sheet of pei, is my current go-to print bed of choice. Holds stuff when hot and lets go when cold - so you never need to remove the plate and flex it to remove print.

At some point I'll probably try gambo's garolite - but at the moment, I have no adhesion problems :-

Looking around - 3d printer adhesive is currently as rare as unicorn drool.
So send your ram.bam.mambo gexxy texk bed back, on the grounds it just does not work - and either go back to your original bed that worked (why change something that works ?)
or get one of these: https://www.ebay.com/itm/324305139528?hash=item4b8217b748:g:PowAAOSwHoNfal0 K