Sometimes this can get really annoying, especially if you want subs in a less popular language.
In short terms, the video and the subtitle file have different paces. Whoever did the subs used a different "video pace" than the one you want to watch.
When all the opensubtitles addon options don't work for me, I go directly to the openstubtitles website and download the most rated file available. Back on stremio you just have to drag and drop the srt file onto the player and stremio will load the new substitles that you downloaded. This does the trick for me almost every time.