On the one hand, I earned around 100-some points in the last day, on the other hand, my total increased by something like 10. Is there some bug?
On Martin Sleziak's encouragement (https://chat.stackexchange.com/transcript/message/45770456#45770456), I'll patch together some in the information in comments to form an answer.
As I read it, the question implicit in the title is really about how to track and understand non-obvious reputation changes, where the net change differs from what was expected. Particularly, the function that enables one to automatically see records of removed posts seems to differ from one stackexchange site to another: on many sites such as MO, you may have to check a box that says "show removed posts" before you can see a record of such that affected your reputation. (Go to your user page, and hit the reputation tab where you should then see a log of reputation changes. Scroll all the way to the bottom of the page where you should see a box that says "show removed posts", and make sure that box has been ticked.)
Posts may be removed for example by deletion of posts (whether by the post author, or the community, or the site moderators), or by deletion or destruction of accounts. For those with sufficient reputation (10k+), a link is provided in case it was a post deletion.
For the record I'll copy over Martin's helpful comments above:
"IIRC if you check the checkbox "show removed posts" on your reputation tab, you should see there also negative reputation changes with links to the posts that cause them. See also: Where reputation disappears and Mysterious one point rep increase."
"I will add one more link, since quid's answer there gives a very detailed explanation: I had reputation of 104 it fell down to 96 the next time I logged in. Why is that?"
The only other issue touched on in comments was about downvoting, and most of the confusion expressed there has been sorted out. (Occasionally I notice the term "downvoting" being used to cover a range of activities, including voting to close and voting to delete, although I'd prefer maintaining these distinctions in terminology, for the sake of clarity.) Igor Rivin was only asking about the downvotes on this meta question -- fair enough, although as YCor and also Gerry Myerson noted, the practice of downvoting at meta tends to be much looser and wider than at main, far wider than for reasons of being "unclear" or "little/no research effort". For example, it is often used to express a disagreement, or a perception that someone is behaving churlishly, etc. I would guess the fact that downvoting at meta is dissociated from reputation change imparts a sense of its being less weighty or consequential, and so it's more liberally applied.
Even if moot for Igor's immediate concern, YCor also noted that answers on main, even if not bad, might be downvoted in order to dissuade others from answering questions perceived as low-quality. If it matters, I (and apparently YCor) expect that's what happened in the case of the question https://mathoverflow.net/questions/304542/oriented-angles-of-two-vectors-in-the-3-dimension-euclidean-space/ at main that was deleted.