These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
There was a literal special-effects failure on the set. The day before the crew was set to "destroy" the London of 1960, they made a huge batch of oatmeal, which would stand in for the lava flow. Unfortunately, there came a very hot day, which caused the oatmeal to ferment! It no longer had that thick consistency, but the effects team had to just roll with it.
Another real life example had Alan Young commenting on his make-up as the aged James Filby failure:
"They made a face mask of me to fashion all that rubber stuff — the old age pieces — all around. On the morning of that shot, I got made up by Bill Tuttle, and as I left, he gave me a little jar of glue, and he said, 'That's in case it comes off,' and I said, 'Well, won't you be on the set?," and he said, 'No, the budget can't afford a makeup man on the set.' So, I had this jar of glue, and that was at 6:00 or 7:00 in the morning. Well, they didn't get around to shooting that scene until late afternoon, and by then I could feel bits of my face falling off, so I'd get the glue out and stick it back on again, but by the time they actually got around to shooting that scene, it was about 4:30 or 5:00. So George said, 'Alan, I can't do any close-up's because I can almost see the glue brush strokes on your eyes.' So, if you remember the scene, it was done in a two shot all of the time. There were no close-up of this old man because bits of the face were peeling off."
Tear Jerker: David Filby's ultimate fate. It's made even worse in a short film done for a DVD release of the movie in which an older George returns and meets Filby right before he leaves for the front. He tries to warn him, expecting to be disbelieved. Filby does believe him... and he goes anyway.
James Filby's fate. In the space of five minutes, George watched his best friend's infant son grow int a young man with a lot of promise, then become an old man who likely died along with everyone else when London is hit by a nuke. And it goes From Bad to Worse when Weena's comment causes him realise that Filby's warning to "Hide until the all clear" has become twisted into the means in which the Morlocks have conditioned the Eloi to walk blissfully to the slaughter.