I have developed a basic app with Kivy but on_release does not work properly on my button bind.  I can get on_press to work every time but on_release works sporadically (maybe one in ten to twenty times) and sometimes on a different part of the screen than you've touched.
I'm pretty confident it's not a coding issue and one of the Kivy devs said it is not a known issue and should work but they haven't said where I might dig deeper.  
In tandem with this, I have been receiving an SDL error in terminal:
INFO: The key you just pressed is not recognized by SDL. To help get this fixed, please report this to the SDL forums/mailing list <https://discourse.libsdl.org/> EVDEV KeyCode 330
This appears on both touch and release.  EVDEV advised to upgrade to SDL2, which I did and it has not solved the error which could just apparently be ignored if not for the spam it creates.
I'm not sure if these two issues are linked but don't know where to start with troubleshooting.
Can anyone please help with what steps I could follow to try and get this resolved?
I mostly want to fix on_release but if we fix the other error in the process then that would be great too.
I am running a Raspberry Pi Zero W, Raspbian Buster w/Desktop and a Hyperpixel 4.0 square screen
Thanks!
I have been having the same problem.  I am using Kivy 1.11.1 with SDL reporting as 2.0.9+dfsg1-1+rpt1 in dpkg.  I have read that this is fixed in a later SDL version but I've not worked out how to upgrade this.  Take care if you extract the SDL RPI tarball, as on my system it trashed the /usr permissions (and didn't upgrade the version as reported by dpkg).
If I run mtdev-test (see google), the touchscreen events come through smoothly.  When running kivy apps, the touchscreen events seem to be laggy, coinciding with the 330 error report.  Press/release seems to work, but motion events are erratic.
With my touchscreen, the error problem can be demonstrated really well with the kivy example demo/touchtracer, which works great with a USB mouse but is terrible with the touchscreen.
Kivy on_release not working on touchscreen - SDL issue?