Good for you. The regional post office in the ATL area is a train wreck, you can look that up easily, and I know from personal discussions with my former chief of police that there was inside stuff happening at the local post office where I lived for many years.
My assessment holds for my geography, your personal experience does not negate that.
I recommend people not mail checks. Period.
It looks like this varies widely by region for sure.
Atlanta is known as one of the “bad ones”.