Why does Mac hang with Photoshop Elements 2019 and Mojave after previewing video clip in Organiser, but only the first time

Hi I have videos and photos loaded into Organiser 2019 on my iMac running Mojave. The problem that has existed in the past few versions of Photoshop Elements and iOS persist . The problem is that after previewing a video clip in the Organiser, the program hangs. Only Force Quit works. I have done the adjustments advised by Apple, i.e  ensure the programs have correct security access and cleared all relevant caches etc. This was all done done under Apple guidance. t worked for a while. Today the problem is back, and seems now to be only on the first viewing of the clip. At this stage there is no image in the organiser for the clip, and I usually get a message saying " Preparing media". The clip plays. You return to Grid of media, and it hangs. Do a Force Quit, start again, repeat. This time there is an image of frame for the video in the Organiser grid. Play the clip, back to grid, and it doesn't hang. As all software is current and supported. i need to get this fixed. It seems lots of people have had various  hangs, and no real solution seems to exist, even though we were promised 2019 and Mojave would be OK. Chris