Do bed magnets deteriorate.

[Roberts_Clif]

Yes

Magnets do get old.
And
If Magnets Get Very Hot or Cold

[Bikeracer2020]

I think I'll have to look at a way of securing the edges that doesn't encroach too much on to the build area.

My usual bed temp is 95 degrees, so not really very good for long term use, and getting a new heated bed or any spares for a Qidi printer sent to the UK seem to either incur very expensive shipping costs, or suppliers such as Aliexpress or even the Qidi store will not ship to the UK.