Due to engineers performing their daily checks and pulling this circuit breaker to be able to check the strobe lights working on GND. A Standard procedure since decades on the type among engineers worldwide.
Using Circuit Breakers as Switches. HERE.
“One thing I note continuously throughout Apollo is the way they cycled circuit breakers, often as a matter of routine operations. In my experience with aircraft systems, circuit breakers are considered as protective devices that should not be used as a switch to turn systems on and off. While it may be acceptable for maintainers to open breakers to make a system safe for maintenance, it is not standard practice for pilots to cycle breakers. We would only put it into a checklist reluctantly, and only if no other way exists to turn off a system.
Since the circuit breaker plunger is held in mechanically, repeatedly cycling it can wear it out. For a system or component that is required to be turned on and off, a Power switch should be used, with a circuit breaker also in the circuit for protection".
Also - From SR111 Canadian Report.
HERE.
1.18.5.4 Circuit Breakers Used as Switches
The use of CBs as switches, either by design, or as a consequence of the system's in-service performance, is not recommended. The FAA guidance on this issue is contained in AC 43.13-1B and states "Circuit breakers...are not recommended for use as switches. Use of the circuit breaker as a switch will decrease the life of the circuit breaker."