[sle70000]

Sure, that would be it. IMHO, if this was truly a Kodi problem, at half of all Windows users would be kicking and screaming here, probably some of the other OS users as well. But that is not the case. Here we have not even a handful cases where properly storing subtitles is a problem. So it's either a write permission issue, outside interference or divine intervention. So far we haven't been able to replicate the problem. 

will someone look into it, if I post logs?
"Play next video automatically" is a fairly overlooked feature, so I am not sure about the screaming and kicking part..
it's not permission issue, since it saves next to the files perfectly fine if I turn it off.  

It's actually a relative path 'issue' . Play next sends relative path to player and therefore can't search for subtitles as there is no title to search with. This is not a Kodi problem but an addon issue. The addons cannot translate the relative path to a title and therefore won't work. Kodi needs to use relative path in order to be able to create a playlist. Unfortunately it's not the answer you were looking for but it's an answer nonetheless.  

If the addon wouldn't know the title it would of fail to find the subtitle. But is not the case. The addon is searching and downloading the correct subtitle for the correct file. It then pass the downloaded file info to GUIDialogSubtitles which decide where to save the subtitle based on user settings(next to the movie or custom folder).
1. When GUIDialogSubtitles is call it search for available subtitle addons and it present a list of them to the user
2. When user is choosing an addon GUIDialogSubtitles calls the addon with parameters: action=search, languages to search for and a preferred language if one is set.
Note that the title or the database id of the movie is never passed to the addon
3. The addon is identifying the playing title and is searching subtitles for requested languages. When finished it passes back to GUIDialogSubtitles a list of found subtitles from which the user can choose. This list must contain the addon ID and the link of the subtitle.  
4. When user choose one subtitle GUIDialogSubtitles is calling again the addon this time with parameters: action=download and the url of the subtitle.
5. The addon is downloading the requested subtitle, store it in a temp folder of its own and pass back to GUIDialogSubtitles this location.
6. GUIDialogSubtitles take the subtitle file and based on user settings(next to the movie or custom folder) make a decission and copy the subtitle to its final destination.
So is kodi who fail to get the correct path and title. You can tell that by the fact that even if the addon is doawnloading and passing to Kodi  a file named correct_title_name.srt Kodi save it as something like 9985.srt. That number is the database uniqueid of the title.

[Tobby]

Just wanted to say that this problem occurred for me too today. Or rather, I noticed it today. Are debug logs of any use our are the ones already provided sufficient?

[HeresJohnny]

I have the same problem and it occurs with both CoreELEC 19 final and Android7 19 final. Share is over NFS. Write access is possible since artwork is downloaded to video folders.

[HeresJohnny]

I've come across a specific problem with NFS, possibly only the Hanewin NFS server. When saving any file its maximum size is limited by the NFS Blocksite defined by the server. The maximum possible size seems to be 32kb in any case.

In the case of saving subtitles this will lead to the subtitle file being saved in a temporary folder in the addon configuration folder under the user profile.

In the case of saving .nfo or artwork the file is saved but it's file size is truncated to the NFS block size. Artwork Dump displays an error that saving went wrong.

I have contacted the creator of the NFS server and asked him to investigate this. I would also ask Team Kodi to check if there might be a bug in core.

In any case it seems to me that the checking mechanism of subtitles add-ons works better than that of core. Writing of files should not occur if the result is a truncated and therefore corrupted file. Maybe Kodi core could be hardened in this respect, thanks.

[Klojum]

An NFS server that can write files only up to 32kB is a problem...?! If it is by design, then so be it. It would still be a strange situation, so the reply from Hanewin would be interesting.

I've never seen such a limitation on NFS storage. If it were to be a bug in Kodi Core, then I'm guessing so many other NFS users would have complained already.