Electrical – 20A home circuit breaker stuck in “TRIPPED” state

Refrigeration equipment may be served from another circuit aside from the kitchen circuits but it is not required.

210.52(B) Small Appliances.

(1) Receptacle Outlets Served. In the kitchen, pantry, breakfast room, dining room, or similar area of a dwelling unit, the two or more 20-ampere small-appliance branch circuits required by 210.11(C)(1) shall serve all wall and floor receptacle outlets covered by 210.52(A), all counter-top outlets covered by 210.52(C), and receptacle outlets for refrigeration equipment.

Exception No. 1: In addition to the required receptacles specified by 210.52, switched receptacles supplied from a general-purpose branch circuit as defined in 210.70(A)(1), Exception No. 1, shall be permitted.

Exception No. 2: The receptacle outlet for refrigeration equipment shall be permitted to be supplied from an individual branch circuit rated 15 amperes or greater.

As to why it is tripping the breaker, I think you apparently have too much on one circuit and the addition of the mixer put it over the top. A GFCI trips if current is diverted outside the normal circuit path and the breaker trips if the normal circuit is overloaded. You may have had the microwave or another appliance running with the fridge and mixer.

Moving the fridge to its own circuit would make good sense in this case.

Honestly, with these kinds of protective-device trips, the problem is often exactly what says on the tin.

An AFCI breaker is designed to look for arc faults, principally in the building wiring. You've swapped breakers around, the problem does not move with the vacuum, it does not move with the breakers, it has stayed with the bedroom. Occam's Razor: it's in the bedroom wiring.

Since wiring problems are almost always at wire ends or devices, I'd preemptively swap every receptacle with a nice contractor grade screw-and-clamp type.