maybe the hardware client side settings to disable them didn’t apply until I rebooted?
No, restarting the machine wouldn’t make a difference for hardware decoding, so it is very likely unrelated to hw decoding
As far as I understand, the problem appears only with one application?
Googling I found this: https://support.xilinx.com/s/question/0D52E00006hprh2SAA/vivado-20201-display-problem?language=en_US. Is this similar to your issue?