Ack. Just applied a fix on the scroll. Not sure what to do with when mobile phone goes to sleep. Will look into it
Regarding mobile phones going to sleep, Wake lock [1] might help, unless you can reduce to 59s since I believe 1m is the threshold (make sure to request within the context of the user hitting "start"). Unfortunately on older mobile browsers [2], the best workaround I found was using this NoSleep library[3].
Source: ran into this same issue when building https://www.phonefreehour.com
[1] https://developer.mozilla.org/en-US/docs/Web/API/WakeLock