I think I remember this happening to me on some pages depending on what was happening.
I really haven't used PHx for some time so I've turned mine off in Plugins. If you really need to use it there is a config setting "log events". Check that it's 0.
If you have already disabled PHx in plugins then it may be an idea to update DocLister.
I wrote a very simple plugin to try and keep the events from stacking up. It may help.
// clear out System Events Log for PHx information events
$query = "DELETE FROM ". $modx->getFullTableName('event_log')." WHERE source = 'PHx 2.2.0';";
System Event: OnWebPagePrerender
That gives you the option to keep some just in case.
Sorry, this may not be as helpful as just stopping it from working.