Hi,
I have application in Swift 4 in MVVMC. After iOS 13 release I have problem with ~2s delay after pushViewController method. It is ok on iOS 11, 12. I've checked build created on xcode 10.3 and 11.2.1 and in both of them there is a issue with that delay.
After a while I've found that one method with setting label.text callef from viewModel was called from globalQueue from some reasen. That caused that delay. I don't know yet why on iOS 11 and 12 that worked perfectly. I had to call that method from mainQueue and it woked perfectly for me. I'll have to check changes in iOS 13 about GCD.