Last weekend I flew my S900 (Hexacopter) and my Daya H680 (Quadcopter) with the recent built of 4.0 on a 3DR Pixhawk. Alltogether around 40 flights 10-15min per flight.
The only thing I can say: FANTASTIC and BRILLIANT WORK to all developers.
I couldn´t find any issue, the flights seemed to be much more stable and smooth than with 3.6.10. I only updated it without changing any parameter. Everything which is important for me worked. Some new functions (i.e dynamic notch) I didn´t test because I was not sure how to configure.
I am very confident about 4.0. So if you want me to participate on beta tests, please aks me and tell me what specific test I should do. I have 8 different Pixhawks/Pixkacks/Pixracers…, so I could do different test if you want.
Thanks again for the fantastic work