I always post tables by copy/paste from Google sheets. Seems to work pretty well.
HTML copy-and-paste glitch

Thanks for the hint. I will check out working with Google sheets.
Still it's strange that chess.com does not allow uncorrupted HTML copy and paste.
I've tried it with the CMS of our chess club's website, and there it works perfectly:
http://dd1852.nl/page.php?i=test:%20wcl%202020%20cross%20table
I've put a lot of effort in nicely formatting a cross table for the World Cities League. However, when I copy and paste it from my HTML editor (Mozilla Composer) to the "New Topic" field at chess.com the formatting is corrupted (see below). In particular, the lower border is broken and the left border of the "total" column has lost its uniformity.
Anything I can do to transfer my HTML code correctly to chess.com? (I can provide the original code if required.)