Have just rolled back to 15.4.0 and the issue has gone./
Please test fully before release or I shall have to bill you for the downtime.
Check with Newtek in case NDI streaming is problematic.
Check compatibility with nvidia studio and BMD decklink drivers.
15.4.1 has an issue that is causing it to not display video. Assume it is a mercury GPU thing but disabling hardware acceleration did not stop it happening. Also test for dual GPU users in case Premiere is getting confused by multiple identical GPUs