I have a 2018 Model 3 and have been running into the problem intermittently for the last month or so. Opening the truck also always works from the app. I always do scroll wheel reboots, plus the service menu power down after each firmware update.
Made an appointment with mobile service and they indicated that my screen protector (tempered glass, 9H) might be causing the problem. In my case when I press the Trunk icon, the text changes colour as it normally would when it works. Mobile service mentioned that you can press the Trunk icon, slide your finger to a different part of the screen and the trunk will not open. They said the screen protector might be causing the same effect to happen.
I provided timestamps and asked if they get coordinate events in the logs to confirm that the finger down event location matches the finger up event location, but unfortunately they said coordinates are not recorded (which surprised me).
They wanted me to remove the screen and test it, but I haven't yet done that. Fortunately, I haven't seen the problem in the last week so I've delayed the service appointment and am really hoping that the problem has just gone away as mysteriously as it appeared.
As an aside, last spring I could only open the trunk from the screen or the app, but not using the latch on the trunk. The trunk harness was replaced at that time to fix that problem.