In Pokemon GO PVP, some taps & swipes are visualized by the game while others, mainly in the switch menu, are not. In cases where part or all of the interface becomes unresponsive to taps it would help to call for a rematch so that plays can be continued fairly, but when these glitches arise they seem to be when the game can't prove you are tapping. In these cases it's beneficial to have Touch Assist (or your phone's variant) turned on to prove your taps aren't registering in the game & not that you may be faking it or be accused of such. Please note, this will really be most useful in remote tournaments as in a live in person tournament you will be able to show the opponent that you are having an issue. As always you should play out a match and then discuss any issues at the end, since if you quit out and have no proof you have lost the game. *Doing this will not help you in GBL as you can't get rematches, but it can also help you learn how to tap in more effective & efficient places to improve your gameplay.
For Android you must turn on Developer Options, which gives you extra settings to control on your phone & must be careful with some of them, but follow along & you'll be able to not mess anything up.
Open Settings & Scroll to "About Phone"
Scroll to the bottom & repeatedly click on the "Build Number" You will get a pop up saying "You are now a developer!" or similar.
Click back to return to the main Settings Menu
Scroll down a bit more to "Developer Options"
This is where you need to be careful if you don't know what these settings do.
Scroll a bit til you see the "Input" section & an option for "Show Touches" turn it on.
Congratulations! You will now see all your touches and swipes until you turn it off!
iOS i(nferior)OS is a little different, you must turn on the whole accessibility suite but, it isn't a hindrance if you know how to place it properly.
Open Settings & Scroll to "General"
Open & Turn On "AssistiveTouch"
Change the "Idle Opacity" to where it isn't as intrusive & you can still see what's happening in your game. You can also move where the AT button sits on your screen, I suggest in the top, middle of your phone where the least amount of Pokemon GO PVP data lives & you are virtually never going to tap there.
Click "Create New Gesture"
Just do a small click on the grey space.
Save & Name it "Touch"
Click the Accessibility Menu
Congratulations! You will now see all your touches and swipes although not as nice and stays on screen at all times, you can turn it off easy by opening the Accessibility button!
Unfortunately, iOS is known to break this functionality in certain updates (sounds familiar) so if this doesn't work currently look out for a new iOS version.