Is it really that deep, just use what works for you man.

Seen that before. Sounds like a weird harmonic resonance with the board's VRM. Old unit probably couldn't handle that specific switching frequency cleanly.

My old Porlex took about 90 seconds for a full cup.

That Florida humidity is a killer for sure. One thing a lot of guys miss is the temperature of the metal itself. If that Civic was baking in the sun all morning, you're putting filler on a hot plate. It'll kick off way too fast no matter your mix. Try parking it in the shade for an hour first, or even wipe the panel down with a damp rag to cool it off. Makes a huge difference in how the filler lays down and cures evenly.

Honestly if the tiles are already loose, that underlayment is probably shot. I had to pull up a whole bathroom floor last year because the cement board got wet and turned to mush. Tbh you're looking at a full redo, not just spot fixes.