Routine presenting multiple stimuli/images not showing on some participants. Erroneous display times

Online issue
I am running a Psychopy experiment where we display 16 pictures (~200Kb each) at the same time in a 4x4 grid from the resource folder. It works well for most people, but for about 20% of Windows users online, the pictures either don’t show up at all or they appear late. Since the grid is presented for 4s, the delay in presentation affects one’s performance. I think there might be an issue with how the pictures load and show up on some computers.

Has anyone else faced this issue presenting multiple images on one screen? Would you have any solutions?