Quick answer: Godot 4 trigger area's body_entered firing on a frame where physics was skipped? Triggers fire on next physics tick; can be off-by-frame.
Quick movement through a trigger; sometimes detected, sometimes missed.
Use continuous collision
continuous_cd on fast bodies. Sweep test through frame; trigger fires.
Or thicken trigger
Trigger area sized so even fast bodies stay inside for a tick.
Audit fast moving
Each fast-moving body that interacts with triggers. Mark as continuous.
“Triggers depend on tick-time presence. Fast bodies may not be there at tick time.”
If your game has fast bullets or projectiles with triggers, CCD is mandatory.