From Jacob Massey-Chase@21:1/5 to All on Mon Feb 15 19:07:59 2021
This is an olf forum but my solution was that I didn't realise that the preceding cell had spaces after the text, that were 'leaking' into the following cell creating the illusion of a missing gridline.
The solution for me was to delete those spaces, or to change the text wrapping so that they were hidden behind the cell/gridline instead of in front of it.
Hope this helps someone looking around for this weirdly specific problem!