Dear jp-psycholojs, thank you very much for you response! I have deleted the loops in first three trial sessions and wrote the path exactly to the file. The last loop - actual experiment, seems to work quite ok, although one more problem occurred - while presenting the video, only audio works, video isn’t displayed (only the background colour is visible). I have checked similar topic (Problem with running video files in Pavlovia - #4 by jonathan.kominsky) where the solution was to encode .mp4 with h264 codec, so I tried this, but unfortunately it still doesn’t work.
Those are details of one of my video files:
I have deleted the experiment and uploaded it again, here is the new link: Karolina Ćwik / test7 · GitLab
Thank you very much in advance 
Karolina