Sudden loss of pedal

fnaramore said

Not a great way to adjust them with the drum/wheel on due to that they are self-adjusting. If they were regular adjusters I'd just do them like I do 356's. Crank them till they cant turn to make sure the shoes are seated and then back them off till it turns well.

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With new drums I like to adjust till I can almost not get the drum on, then set the E brake and release it.
Then check them again.
The E brake will set and center the shoes just as well as stepping on the brake pedal.

The answer to your original question is probably air, because 99% of the time that's what it is.
Air can get by wheel cylinder seals when there isn't any pressure on them.
You need to bleed the right rear first, and then the left rear.