Update: So I decided to play from a manual save point I made 20 minutes before I found this portal, and redid the whole thing - it now works again.

Very odd - thank you again all for your help!

I'm having issues with the game not saving or loading after a while of gameplay. The only fix I have found is restarting the game.

This sounds like software conflict frankly.

I had problems when using Chrome. But since others didn't I can only assume it was one of the add-on to Chrome I was using.

My problems disappeared when removed Chrome and use Edge.

Suggesting to start by removing some other software, just to check. Browsers are the obvious start. Others include stuff which runs in the background. Ccleaner for example is great, but only the portable version. Installed includes some other stuff which claims to do this or that and which may cause conflicts.

Addition. There are aslo a number of hijackers doing the rounds. I don't want to panic anyone but it is in the nature of these things to prepare themselves for the attack, long before.

Run PrivaZer, Ccleaner portable and ADWCleaner from Majorgeeks.com

Keep backups of your important docs ect. Don't visit porn sites, especially videos and good luck.

I found the issue just then. Running the game through GOG was the issue. Once I launched it on its own it saved fine and had no infinite loading.

Excellent. Thanks for getting back.

I confess I don't use the GOG interface thing either.