My hypothesis: the first bleed wasn't actually good, but the air was trapped in the reservoir. So when you pulled the lever, the piston closed off the reservoir and the air was outside of the pressurized system, so everything felt fine. This probably would have revealed itself with further riding and getting the brakes hot - the air would have worked it's way out of the reservoir soon enough.
Then you tightened the hose some more, and maybe just by virtue of fiddling around at the master cylinder, that air that was trapped in the reservoir made it's way out into the line. Now the air is inside the pressurized system, and it feels spongy. You bled it, got the air out, and all is well (assuming there isn't any air still hiding in the reservoir).
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