Upgrading project to Unity 2020.2.0b4 has basically made it unresponsive, in the editor player as well as in builds.
Here are some errors that show up in the console (dozens of each):
Internal: JobTempAlloc has allocations that are more than 4 frames old - this is not allowed and likely a leak
Internal: deleting an allocation that is older than its permitted lifetime of 4 frames (age = 11)
I have upgraded from 2020.2.0b2 to 2020.2.0b4 and I get at least the same warnings.
For me it happens every time I enable/disable a UI element (which gathers some data from a ECS system OnEnable, dunno if this could be related). It was no problem in the old beta.