To reproduce, I’ve set up an UE4 project “pinch bug demonstrator” that you can find here:
https://github.com//Blueprint-Recipe-Repository/tree/master/PinchBugDemonstrator
Deploy this to an android device.
Then put first finger on the screen,
Then place a second finger on the screen.
Then move your second finger towards or away your first finger so that the numbers gets ridiculously big or ridiculously small. (around 0.1 small or 50+big)
Lift your second finger, then place it back.
What should be the expected pinch axis value on this? One might expect the pinch axis value to reset to 1.0 (or due to hand movement margin of error, jitters around 0.9xxx and 1.xxx or something). When you do this test repeatedly, the numbers will jump around depending on whether you increase or decrease the distance of your fingers during your pinch.
I was unable to cleanly workaround this issue by ignoring the Input if axis value is equal to 1.0 as the other user has stated, and instead had to workaround by disabling pinch ability when the second finger is released until the first finger is released, and only then pinch ability is enabled again.