It really should work with the 3000 processor because the AGESA version in it, 1004b, was 'made' for it. B350 was originally never going to work with Ryzen 3000 so AMD opened the AGESA to it was kind of last minute and it was put out as a 'beta'. So if it wouldn't work with something it should be the older CPU's since, being BETA, it was probably not well regression tested.
And lastly, I have no real idea what OP did to prove out it works with it. It could boot, then once he starts making changes to settings it cold bricks on him or is otherwise unstable. It's BETA, after all and it's quite apparent something about it is not very reliable since it doesn't work with his 3600.
And what's odder still is that I've seen others have their BETA BIOS working on other MSI B350 boards with their Ryzen 3000 processors (although not Bazooka's, to be fair).