The question was automatically deleted by the Community♦ bot:
Apr 11 at 0:16 history deleted Community♦ Scheduled: RemoveDeadQuestions
It had a score of $-2$, was more than 30 days old, and had no answer. Such questions are automatically deleted network wide. Your question was never closed, old negatively scored questions without activity are ...
The system will automatically delete closed, unlocked, and non-migrated questions that have zero or negative score, have no positively scored or accepted answers or pending reopen votes, were closed for any reason other than duplicate nine or more days ago, and haven't been edited in the past nine days.
(The timeline's a bit off since you deleted ...
Yes, comments are often removed by moderators without notice, often in response to a flag on the comment by some user. Indeed, this is one of the main activities of moderators.
Many of these removal are also harmless. The reason for removal is merely that the comment is not (or not anymore) necessary, at some point this was called "too chatty" it now ...
From the MSE deletion faq:
If the question is more than 365 days old, and ...
has a score of 0 or a score of 1 with a deleted owner
has no answers
is not locked
has a viewcount <= the age of the question in days times 1.5
has 1 or 0 comments
... it will be automatically deleted.
(Actually, the above is quoted from an answer by ...
The question was auto-deleted when it reached negative score again. Not to forget: that you run this risk was pointed out to you some time ago; you dismissed this advice. Here is a link to the question https://math.stackexchange.com/questions/1183087/integral-closures-of-algebras-of-finite-type-over-the-ring-of-algebraic-integers
I think that it is relatively safe to assume that the tasks which run daily are scheduled on the same time. (Similarly, scripts which run once a week/once a month are most likely scheduled on the same day of the week/month and on the same time or at least near the same time.)1
So if somebody noticed on a few occasions that roomba deleted questions around 03:...
You can find the details here:
Enable automatic deletion of old, unanswered zero-score questions after a year?
The gist is that a question closed for 9 days, with a non-positive score, no positively scored or accepted answers is deleted automatically if it hasn't been edited for 9 days.
(Also relevant: How does deleting work? What can cause a post to be ...
This answer on meta.SE gives the criteria for autodeletion, and this question met one of them. Although one of the other criteria depends on the score being negative, the one for closed questions without upvoted or accepted answers, etc., only requires that the score be nonpositive.
Deleted questions are only about a fifth of all questions (about the same is true for posts, and also when restricted to, say, calculus and last year).
Thus, performance and resources are presumably not a major concern (even more so as deleted content is not really deleted).
Arguably there is even not all that much impact regarding discovering good ...
The posts you link to concern auto-deletion and deletion by OP. However, posts can also be deleted by votes of 10k+ users (and moderators).
See How does deleting work? What can cause a post to be deleted, and what does that actually mean? What are the criteria for deletion? for details.
It is not uncommon that (closed) questions are deleted by votes of ...