I’m not sure I follow the URL you are referring to, but the symptom you mentioned usually happens when something has flushed permalinks at an unexpected point in the request before EE could adds its rewrite rules.
So then the event links and any of the ‘pretty’ links /events/{something} for example, stop working.
Flushing permalinks will fix it if that’s the problem by going to Dashboard -> Settings -> Permalinks, making no changes and just hitting save.
As a one off its not cause for concern but if it continues to happen we can start some additional troubleshooting to narrow it down more.