It looks like a directional issue.

Yeah... All glass panes seem to have this problem when we added CTM. We are looking into a fix for both issues, sorry for the inconvenience! Connected textures do be funny sometimes.

Another one:
(Depends from which side you look)

No only GLASS_PANE_7 also GLASS_7 have the same inconsistences

A lot of blocks

It seems all of the blocks with connected textures are bugged; several of the stone types randomly connect/disconnect when other blocks are placed around them.

is still present in 1.18.2?

Yes, last time I looked. If there's a recent update then I haven't seen it with the update yet.

It seems all of the blocks with connected textures are bugged; several of the stone types randomly connect/disconnect when other blocks are placed around them.

Bit late, but had the same problem. Seems to be bc of Rubidium, see CTM#168. You can press F3+A to temporarily fix it. This issue is not related to that however, since that does nothing for panes.