Disappearing claps have been an ongoing problem with Medium for years, usually but not always when you clap from a mobile device.

Medium seems unwilling or unable to definitively address the problem. Like you, I suspect that if claps are not registering for mobile devices, then read time probably isn’t either. But Medium has never been transparent about what’s going on, normally just denying that anything is happening, even though we see it happening with our own eyes.

They do say, by the way, that clap rationing is not happening. You should be able to clap as many times as you want for any story or comment without affecting future claps.