When you try to connect the profiler to a player built when a more recent version of Unity, one out of two things can happen:

1. It just works (within certain limited release version I presume).

2. It does not work, but you don't get any proper notification about this, just various "random errors" printed to the console.

One example of such a thing "Unknown profiler data message in session block: 62, previous message was 1"

It would be nice if there was a clear versioning of this data stream, both for live connections and for loading saved profiling data, with some obvious feedback that the user is too far apart on versions.

Afaik this has been the case for a long time and is not a regression. The case I was concretely seeing this in today was a player built with 21.2 and mistakenly trying to attach to it from 20.2.