Pageimage::size() stopped working - specific PHP module required?

[JayGee]

We have a client's Processwire site where the Pageimage::size() method has stopped working. It's creating small white PNGs in the assets folder instead of the resized image as usual.

Their hosting was recently upgraded and switched to PHP 7.4 and I'm wondering if a they've removed a PHP package or changed a server config to cause this.
Does anyone know if the image resizing functionality requires specific PHP modules I need to check for?

I've checked the folder permissions on the server - this all looks fine.

TIA,
J

[JayGee]

Solved: PHP update reset the memory limit too low.