Display MoreI believe it's a bug in the 8.2.4.X version.
It happens where you try to play a movie that is in a folder shared on the network by SMB (Samba).
I've seen 3 possible solutions:
1. (the easiest which is what I do) Use network sharing system NFS instead of SMB
2. Something about storing the subtitle files in a special subtitle folder, separate from where the movie is located. You'll have to search the forums, I don't remember exactly how that works, but theres a libreelec setting about subtitle folders I think.
3. Something about the "Version" of SMB. Apparently SMB has versions which is an advanced setting. I've also seen this somewhere in the folders but I'm not sure if it's an advanced setting of Libreelec, or where the movie is located (like a Windows setting, or a NAS setting)
Indeed, moving external subtitles from smb share to an SD card folder works.
I also found that it can work if you mount the smb shares with ssh in Libreelec (see Mounting network shares) and not Kodi (thanks to @frequenzy and vinbot3000 )
Conclusion: if you experience crash with external subtitles try to mount your smb shares with ssh.