I would suggest testing if curl or Kodi/curl api is the issue. Kodi Piers (LE13) is in development presently with curl 8.13.0. If there is an issue it would be the right time to get it fixed at the source.
From LE - something like -
curl -k --user myusername:mypassword ftps://ftpserver.mine
and check that it is showing you the files you expect, they are accessible ….
- and why / what are the missing files?
What is the common pattern? E.g. Is it path length…. Is it special characters?
if a curl issue, then needs to be raised with the curl team (they release approximately every 2 months)
If a Kodi issue then will need to be raised on the Kodi forum with a reproducible case.
but first best share debug logs will be required to analyze further with the current LE13 nightlies.
Also the results of the “locally executed curl”