Difficult one... can be a false positive.
I (pers.) do not have that issue.
Step 1 (did a check myself also) is the adviced 'compare' the files old vs new to each other.
Since about a good month ago this file has had changes.. so yes old vs new are different.
Could be it is a server side issue, or php ( so could be a bug inside file due to your used system; it is a month old (change) and no other reports made...so could be a guess here).
If you have an old one present, overwrite the newer one again ( single file) and see if that triggers....? If yes than this could indeed be a bug.
Helas no further to comment here as options/reasons are too 'broad' .