Changes:

1) Partial fix of a bug with updating reply message: https://bugs.telegram.org/c/179 (by "partial" I mean that only one part of this bug was fixed)
2) Fix of the dark themes bug based on the provided suggestion: https://bugs.telegram.org/c/923

Full description: https://github.com/sfilmak/Telegram/blob/master/SubmissionChanges/report.md

Video showing issue with the first solution attached to the next comment.

Video showing that the first bug was fixed partially.

Okay, maybe, it would not be counted as a part of my submission, but I found out how to fix the first problem by adding just a single line:

editingReplyObject.forceUpdate = true;

You can see where exactly it should be placed in the code on a screenshot. It seems to fix the bug completely, but if you will found any other issue with my solution - please let me know in the comments here.

Total fixes: 2
Correct fixes: 0

Unfortunately, all the implemented solutions cannot be considered correct. 

#1: "In reply to" preview isn't updated when the message is edited." The chosen approach when the app consequently performs the check of all the messages is non-optimal.
#2: Defining wherever a theme is dark or not. Irrelevant change that duplicates the existing app functionality instead of using it directly.