timelapse videos rendered from 3 months ago are now not playing back normally. The video repeats itself. e.g. instead of playing back the 30 seconds of the video it repeats the sequence over continuously until i stop it. What do you think might have happened here?. thanks.

Is this happening when you play in LRTimelapse? In this case you might have selected a part of the sequence, then it will play and repeat that part.