The beta won't be considered stable until it's no longer beta. Can't say yet when that will be.
We might backport this fix to 4.2, as it's pretty nasty. I'll check with the team.
Strange behavior after AddAnimation on Empty track under special conditions
Well, to sum it up. I removed all calls to Update(0) and refactored these places to with better understanding what Spine is doing. So it is not a black box anymore for us. Thanks for helping me with that! Now a lot of things seem obvious, but e.g. playing empty animations for proper mixing is nothing easily understandable.
And still, I found a runtime bug 
Next time I will directly try to isolate and understand what is going on instead of quickly hacking it with Update(0) call.