In video mode, when you change the frame rate, the previously configured shutter angle will jump to a new value. As well, you can’t change the shutter angle as it’s locked.
A workaround to this issue is to select a different value to adjust and return to the value you would like calculated for you.
For example, I want to know the T-stop so the T-stop value is red. If I change my frame rate from 60 to 23.976, I would press and hold the ISO or Shutter angle value, and then press and hold the T-stop value to ensure it’s highlighted in red again. After this, I’m able to change the shutter angle back to 180 (or whatever it is that I want).
Recreating the problem
1. Power on device
2. Launch app
3. Click on the purple tile (default configuration after pairing the device with the Android phone)
4. Toggle to video mode
5. Press and hold T-stops to have the app calculate the appropriate T-stop value
6. Change frame rate from 60.0 to 23.976 (or any other frame rate)
The shutter angle will have changed and cannot be adjusted until you attempt the workaround above.