You know when you return to a manuscript that there will be language to tighten or heighten, but then there are the errors that make you wonder why you don't fall down more:
(in no particular order...)
Your main character's height changes.
Yes, this has happened to me. He started off very tall and lost about 6 inches somewhere in the last third of the story.
You intended to drop a small but vital clue early in the story.
Intended is the operative word in the previous sentence.
Inconsistent character names.
Yes, I know about 'Search and Replace'. I have no explanation.
Rooms varying locations.
When you're writing a mystery taking place in a large house this can happen. I drew a map after discovering the movable rooms.
A character having favourite phrases.
I thought it would be endearing. I discovered it was irritating. Too much, too much.
A wise character who never makes a mistake.
Dull, dull, dull.
The rhythm of characters' dialogue radically altering for a few pages.
Rather a large uh-oh.
The pace (usually somewhere in the middle) slows to the speed of a sloth on a slow day.
When writers curse about 'the saggy middle' they're not usually referring to their waistlines.
Scenes tipping over into melodrama.
Drama is good. Melodrama makes me roll my eyes. If I'm groaning, I shudder to think what someone else would do.
A scene which took ages to write and you adore.
Unfortunately, it does nothing for plot or character development. Agony ensues.