Same issue here, it's been terrible for a few weeks now. It's worse when I'm on my iPhone on Safari and seems directly related to huge, all-singing and dancing video ads. If there is an ad that has a banner at the top and both sides, all with separate moving videos, plus other whole-page moving ads in the body of threads - which happens so often now - there's absolutely no chance of reading the thread without it constantly crashing and reloading.
Scroll the thread? It reloads. Have the temerity to enlarge the view? It reloads. Repeatedly. Want to turn the phone on its side to view landscape, so you can enlarge the text to read it (hello varifocal contact lenses) and not scroll back and forth constantly? Reload, reload, then get a message the page repeatedly reloaded so Safari gave up and it can't be viewed.
And don't get me started on the bossy instructions for me to 'rotate your device' when I don't want to, and when it's only for the purpose of an ad being shown to me.
It's making the site a real pain to use, not a pleasure anymore.
I have no problem whatever with being shown ads, if that's the way Mumsnet want to make money, then good luck to you, I'm all for it. But the site does need to be usable.
Off the top of my head, some of the ads that have caused the most problems are:
Bronco Stop
Uniqlo
Co-op funeral care
That advert for something or other (something financial) where some twats dressed up as sheriffs jump up and down gurning, finishing with a big, phone-screen-long picture of a sheriff's badge.
Oh, and when the thread is interrupted for a whole page ad, the site jumps, so that once being subjected to the ad is over, you're not where you were when you were interrupted, but are several posts above or below instead, so you end up scrolling up and down to find your place and have the ad play again.... 😡