Footnote separator line changing randomly

I have the thickness for the line set for 0.25pt on both right and left pages, but if I have multiple lines in the footnote it changes thickness. Here is the pattern:
Number of lines: 1 - thin
2 - thin
3 - thin
4 - thick
5 - thick
6 - thin
7 - thin
8 - thin
9 - thin
10 - thin
11 - thick
12 - thick
13 - thick
14 - thin
… up to 18 - thin
19 - thick
20 - thick
21 - thin
22 - thin
… up to 25 - thin

However, when I export it as a pdf it has an entirely different pattern.

This issue came up years ago and was not resolved:
“Well, a few months later and I still have this issue. I’ve tried everything with page styles, indents, Apply, OK, and everything else and I still have different widths of footnote separator lines. The differences are preserved when I export to pdf, so it is not just a display issue. Please someone help- it looks so unprofessional!”
That was in 2014/06/04.

I would think that footnotes would be used often enough that something like this would not go unaddressed.