After upgrading from Premiere Pro 2018 to 2019, I am getting dropouts in the picture of my exported sequences. No such defects exist in the original media. I select sequences in the project window and select "export media" to create a queue in Media Encoder. All sequences encode with no apparent problems. Checking the exported media afterwards, there are dropouts, or artifacts, in the picture throughout. I solved the problem by reverting back to the 2018 version of Media Encoder (but I had to export sequences one at a time). Here is a sample of the encoding problem.
Do you have the latest drivers for your video card? To check, go to the manufacturer's website yourself and manually compare the latest driver number for your card against what is installed on your machine.
Have you tried Neil's advice yet? Report back after trying that. It certainly could not hurt!