Double tap requires very precise touch input
The setting gtk-double-click-distance
is set to 5 px by default. This is rather difficult to reliably perform on a touch screen device like a phone (I tested it on Oneplus 6).
As a quick fix, increasing it to 15 px on application startup improves touchscreen reliability on this particular gesture a lot for me.
In general it would be nice if gtk had different settings for mouse and touch so that rapidly clicking neighboring buttons with the mouse doesn't accidentally register as double click on the first button. If such a separate setting existed it might make sense to even set the gtk default touch distance a bit higher, maybe to 20-25 px. That should be enough even for rather imprecise taps.
Edited by Fina Wilke