Hi Piet,
The problem is that the previous behavior was not intended - it was never supposed open a cell bubble on tap.
Cell tapping selects a single cell and fires TimeRangeSelected event. You should be able to use TimeRangeSelectedJavaScript to invoke a bubble manually when needed:
<DayPilot:DayPilotScheduler
TimeRangeSelectedHandling="JavaScript"
TimeRangeSelectedJavaScript="if (navigator.userAgent.indexOf("Mobile") !== -1) { new DayPilot.Bubble().showHtml('bubble text')} else { /* ... */}"
/>