Three weeks seems like a long time to chase a spalling slab when the answer is usually staring you in the face. Most of the time it comes down to water, not some mystery mix problem. If your downspouts dump next to the garage or the grade slopes back toward the door, that water sits under the slab and pops the surface off when it freezes. Everyone wants to blame the concrete guy or the mix, but nine times out of ten it is drainage. Patching the top without fixing where the water goes just means you get to do it all over again next winter. So what was the actual dumb thing you found, because I have a feeling it was a lot more obvious than you are letting on.