BO product error

[CJH]

I've found that I cannot edit any product in BO 7.4.4. There's some strange error here (previously everything worked fine), in that if I go to a product the combinations have disappeared, the images likewise, and the Summary and Description fields both contain their correct text, but they show all the html code as well. If I change anything, even taking the page/product offline, it says it saves but nothing happens (the product remains on sale, and if I return to the page it is indeed online again). in BO no search works, eg. in modules. Website still functions okay, but I cannot make changes to it.

I was running with php 7.1 - updated to 7.2 with no change. Any ideas for what might have gone wrong? What I can check or find out to solve this?