WP_Filebase 3.4.4 fixed most of the "Ajax not working" issue.
But look at https://comptonshawford-pc.gov.uk/parish-council/governance-documents/e-documents/
In Filebase settings, Inline Add is checked (In each category display actions to add a file or category).
the +Add Category / +Add File links are shown in some folders but not others (for example, Minutes).
I have tried this with Late script loading checked and not checked, and it works the same (no Add File for some folders).