This triggered a repressed memory. I was once on an ops team responsible for an application that had been turned over to us written in Java. The application ran in Tomcat, and prior to turning it over to us, the external vendor had "helpfully" built some monitoring and alerting for the application. One of the metrics they monitored was how many errors per minute and per hour were happening the application's logs. When they turned this application over to us, they did not properly hand over the monitoring system or even tell us that it existed, and it was sending alerts to another external vendor team which had no association to my ops team.

Several years went by... then because we finally had the time our ops team decided to audit and improve this application, including rewriting significant portions of its code as was pretty typical when we took over an application built by an external vendor. Long story short, we resolved almost all of the errors by the expediency of simply correctly interacting with the database behind the application instead of relying on whatever horrific dumpster fire output to the DB that Hibernate was doing. That's when things got super interesting, because the external vendor team that was receiving these monitoring alerts (unbeknownst to my team) had more than 100% turnover in the intervening period of time, having lost all knowledge about this, but suddenly starting getting a bunch of critical urgency alerts going off because the application was no longer emitting the amount of errors expected for the alarm thresholds. This ended up triggering a massive company-wide incident call, even though there was no external customer impact. I'm leaving a lot of details out, but let's just say it sucked up days of my life and was a massive waste of time for all of that.

Fun example of fixing something and causing an "issue" because behavior changed from expectations/baseline.