iPhone 14 Pro Max, (also previous 12 Pro Max) latest IOS and Lightroom. Phone Volume Control, ProGrip or small remote trigger. First of all, I have finally narrowed this issue down to Lightroom Mobile.
ISSUE - Volume control direct or via Bluetooth does not operate the Lightroom camera shutter. When using my iPhone as my camera (video and still) I mostly use the Lightroom Camera. However I have always had an issue when using the volume button and Bluetooth device to trigger the camera, but it felt weird as once it started working then it was fine, (always fine with any other app). I have finally been able to reliably replicate the issue.
SYMPTOMS. When Lightroom and the camera is open and the phone goes into lock mode the volume control takes time, undefined but greater than 10 seconds, with multiple volume control presses when I bring the camera out of lock mode to start working.
This never happens when first opening the app and go to the camera. Always happens when the phone goes into lock mode and then I bring it out with the Lightroom camera window still open. This always happens when the phone goes into lock mode, after Lightroom is minimised then I bring it out of lock mode and maximise Lightroom with the camera window still open. Never happens when I minimise Lightroom with the camera open and then Maximise it with the camera open. Never happens when I open or maximise Lightroom and the camera is not open and I open it.
ANNOYING BUT REPEATABLE FIX Simple but irritating as it is only an issue with Lightroom. As soon as I unlock the phone close and open the camera. Works every time.
ADDENDUM I have just repeated the test and before opening and closing the camera i waited over 1 minute pressing or hold pressing the volume control repeatedly.