Issue
A breakpoint never catches an error that occurs immediately during startup or a fast state transition.
Cause
The debugger attaches too late, the wrong execution context is selected, or the code runs on a different client or server.
Fix
Set the breakpoint before starting the session, confirm client versus server context, and add structured temporary logging around the state boundary. Use the current ScriptDebuggerService beta only in controlled tooling and do not ship invasive debug behavior to players.
Verify
Reproduce in a minimal local-server test and confirm both the breakpoint and log identify the same transition.
Official Roblox Studio debugger recap
#1
Original Heliotrope guidance with authoritative Roblox sources.