I am having the same issue (Vero 4k+) and found this thread while searching for a solution.
In my case videos are stored on a Synology NAS, accessed via SMB3, all movies in a share called “videos”. The username I use to connect to the NAS has read and write access to this share.
On the “videos” share I have a subfolder movies with every movie in its own subfolder.
- I removed all access for this user on my NAS and lost access to all movies (as expected), re-added read and write access after and rebooted everything. Just to confirm access rights really work.
- like the OP I have also tried saving to a custom folder, that does work. I chose the movies folder in the root of “videos” and I can see the file being saved there. So that’s on the same share…
Not a very advanced user so some of the stuff above I don’t understand. Full log attached (first attempt after reboot is when set to “next to videos”, then I change to “custom folder” and try again. I finish by setting it back to “next to videos” an trying that one more time.)
https://paste.osmc.tv/ejixizevid
Note: found a bug with a related issue: Subtitles not saved with video if "Play from here" option is used · Issue #18128 · xbmc/xbmc · GitHub
However in that case subtitles are not saved when using “play from”. In the test above (log) I also used play from. Just did a check on another file playing from start and still have the issue, so my issue seems to be different