From what I understand from what you wrote and others in the forum, some touch screens use touch events (that Xojo does not support) and other touch screens manage/use touch+clicks.
I don’t see you mention the manufacturer of your touchscreen.
My guess is that William’s touchscreen send ‘mouse clicks’ too when he touch the screen and Xojo respond to those, and your touchscreen may not send those clicks.
Can you provide what you use on that Issue and maybe you can test with what Xojo is using?
Of course I may be wrong as I have zero experience with this. This is just an idea after reading some of your posts and what Björn posted here: