Flickering occurs when presenting stimuli on Pavlovia

URL of experiment: Pavlovia
OS : Win10
PsychoPy version : Psychopy 2020.1.3 (Python 3.6.6)

Description of the problem: In psychopy system when I test it on my computer the programme works fine. However on pavlovia, when the images are presented it looks like a black screen is shown in between presenting the stimuli causing them to “flicker”. This did not happen on psychopy.

What are you trying to achieve?: I am doing a visual search/active inhibition task. I show a fixation point (for 1 second), then either a square with green arrows inside or a empty square (for 500ms) and then either just red arrows in the square or green and red arrows in the square.Participants then have to press either ‘a’ key or ‘l’ key to say which direction the target arrow is pointing

What did you try to make it work?: I tried to use the advice provided on this post Online experiment issue: Fade in of image flickers and adapt it to mine so I didn’t get a fade effects by putting frameN/1

What specifically went wrong when you tried that?: It still flickered on psychopy

Many thanks for your help, this is my first time using psychopy so I am very much a beginner so any help would be gratefully received