I have loaded up my map in the new mod tools but sadly there is an issue where all surfaces, apart from volumes and caulk surfaces are bright white. This is after rendering the lights. In game everything is bright white.

It looks like this in the editor:



I don't know if anyone else has this problem but I've looked on the steam forums and here and no-one else seems to have the same issue as myself. If anyone knows what is going on here, do you know a fix? thanks for your time

You 100% made an SSI and saved it in an original GDT from APE, when updating the update replaced all the stock GDTs and so you've lost your SSI+Skybox, you need to remake it!
Next time try to make an abit of making your own GDTs so in case of updates you don't lose saved stuff!