Harbor Freight Fuses

I agree. This could go either way, and it's possible that the fuse was out of spec BUT............

When a fuse has a problem, IE an internal loose connection, usually the fuse just blows because of self--generated heat

If the fuse was "out of spec" then nothing much should have happened, unless the circuit overloaded, so I guess that's possible.

My first "jump" is that there's a bad connection at the fuse connector, and or the circuit is severely overloaded.