Zoom in as close as possible on the split between the two clips.
My guess is that there is a third, tiny clip, possible just a single sample, between the two clips.
There “may” even be a “zero length” clip. Zero length clips should not occur, but a bug has recently been found (and now fixed) where zero length clips would occasionally occur.
The easiest way to fix that is to “join” all of the clips across that boundary, then split it again so there is one clean split (see: https://manual.audacityteam.org/man/edit_menu_clip_boundaries.html)