Thank you! The main problem of this build (20Jul2019) is frozen preview.
I will try to explain this preview freezing issue in some more detail:
It happens when focusing. Unfortunately, focusing while in video mode is not reliable enough. To achieve precise focus (absolutely important !!!), I switch to photo mode. This allows me to get a very detailed 10x magnification and I can focus precisely either manually or by pressing the back button. Once I have achieved perfect focus, I switch back to video mode to start recording and here is where the trouble happens. Preview changes to stretched and freezes upon pressing the record button. The only way out of this situation is to turn camera off and on again. This wastes a lot of time and the moment is gone.
Another bug:
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Camera freezes badly when trying to switch to Dual ISO while in video mode. Not even a battery pull helps. The only possibility to activate Dual ISO is to turn camera off, switch to photo mode, turn it on again, activate Dual ISO, turn it off again, switch to video mode, turn it on again and then you can start recording in Dual ISO.
Both of the above instabilities are well reproducible.