I believe the issue is present when using 5.4-rc kernels (which contain newer HDMI code) and vendor u-boot, and it is not seen with older <= 5.3 kernels or when using mainline u-boot with the current 5.4-rc or newer kernels. In other words, even if you restore factory u-boot to the device you’ll hit the problem. It is definitely present for me on VIM3 and VIM3L using factory u-boot and 5.4, and the issue first appeared with 5.4. I have been meaning to try reverting the simple framebuffer changes to see if that makes a difference, but I’m tied up with day-job work and don’t have time at the moment.