Shared ERP credentials between dev and prod silently broke user authentication

A production application began returning authentication errors for real users even though all infrastructure health checks showed normal status. The root cause was traced to a development activity that generated a new login against an external ERP, which shared the same credentials as the production environment. Because the ERP vendor did not isolate sessions per environment, creating a new session likely invalidated the cached token that production was actively using. In one instance the outage went undetected for days, as background jobs kept running but returned zero records with no alert triggered. The incident highlighted a critical distinction: technical health — processes running and endpoints responding — does not guarantee operational health, meaning the system is actually delivering its expected business output.