Hi,
I found out that with the upgrade to preview.15/preview.16, clicking a button quite often in a short amount of time has the effect, that no events are fired from then on. This was definitely not the case with preview.14.
There are no errors in the log though, it just silently stops firing events. I use the ‘old’ input system btw.
The following video highlights the issue:
The example uses a plain button without any click handler to ensure, that the error is not in my code.
I figured out the root cause of this.
I use two different Panel settings. One for tooltips with Sort Order = 2 and one for everything else (Sort Order = 1). Besides the Sort Order, the settings are identical.
I debugged the EventSystem and at some point, it selects the wrong panel settings:
To resolve the issue, all my UI elements now use one Panel Setting and I use “BringToFront”/“SendToBack” instead of “Sort Order”.
Hey @magnetic_scho , great that you got it working (and also that you’re using a single PanelSettings, which is preferred for performance anyway), but there seems to be a bug with event dispatching there that we’d like to take a look! Do you have a simple project you could submit to us through Unity (Help > Report a bug…) so that we could check that out? Thanks in advance! 
This thread might be related ClickEvent no longer reliable on Android device in preview15, preview16