Plex app stops responding but still playing video



I've got the Plex app version 3.2.20-25990c77 (5/10/2017) running on my old Surface 2 and every time I start the app it works ok for maybe a minute or two and then it starts responding. The video is running but the sub get stuck on the last working sub picture. It is not possible to pause the video or do anything. This happens all the time and it's about this for lik 4-5 minutes.