for the last year or something I've had a theory about the network issues. During the last 3 exams I've taken I've tested this theory and now the conclusion.
It seems you get the "Network issues" error when you scroll using the mouse wheel. I dont know why but if you dont use the mouse wheel to scroll you can work without issues but as soon as you start scrolling you get that error. This was tested during 2 exams (2 times ex425 and 1 ex280 v4.2) on 2 different kiosk systems on 2 different exam centers (Covid limited my exam tries) - I can provide the exam centers names.
I dont know where to direct this, I've put this also in today's exam feedback but I decided to put it here also because it would be also helpful to other candidates.