@BeckyAMumsnet I have to ask - has someone been trying proper user testing? I mean, a standard set up with no ad blockers on, on a "normal" home type device with standard home security levels, not using the Mumsnet network (which I assume will have high levels of security etc.)?
I know that not everyone is having these issues, but enough people that means with enough of your techs & staff testing under typical user conditions you may well see the issue happening. As @TwentyTwentyFive says above, there isn't really anything to see when this happens just that suddenly the screen goes blank for no apparent reason. There's no time to see anything happening, and the timings of this is so erratic you couldn't really schedule when would be a good or bad time to try.
As an example of how erratic the timing can be, in general the issue seems worse at peak times. But this morning everything for me was fine until around 6:45 - 7am, then suddenly the screen started blanking. It took me about 4 goes to read a single long-ish comment on a thread. I moved on to another thread in the same forum, no issues. Then the next one, had a blank.
Then I wanted to post a comment - total of 10 lines in 4 paragraphs (on a PC). It took me around 5 goes to get the first single line paragraph written. Then I managed to write the rest of the post with no more blanking. Each time I had to use the browser back button and go back to the page I had been on when I started the post, it had saved where I was up to in writing the post.
Moved onto another thread (different forum) - amount of blanking became so painful I gave up.
However I've now typed this entire long post without a single issue!