VLC won't stream video file if subtitle file is present

[Heinzz]

I just installed a NAS device and trying to stream video's on the Ipad from the NAS. It seems to go fine if no subtitle file is present (I can play mkv, avi, ...), but things start to go wrong when there is a video file with an accompanying srt file. At the bottom of my screen, I get a small "pop-up" and I can see that VLC is cycling through the video, trying to play them.

In the same folder, I copied a video file with subtitle file (srt) and a video file with the subtitles embedded. I first clicked on the video file with subtitle - VLC could not play it, but went on to the next file (the one w/o subtitles) and it started playing that with no issues.

what am I doing wrong here?