"Demineralized" water killed my 510-Pyro - a word to the wise

Boiling also reduces absorbed oxygen.

reverting to the water which worked will probably resolve your problem. If it ain't broke, don't try and fix it.

Tap water can vary seasonally even where it's relatively very good. Many places it is not. For instance, after major rainstorms my own water
can pick up a bit of color or mineral content. Most of the time it's piped in as snowmelt from mtn reservoirs, but sometimes in winter, that
can get offset by runoff into local coastal secondary storage reservoirs. When in doubt, I mix developers with distilled water. I also have
line filters in place going to the print washers, to catch any little bits of sediment. I also use distilled water when doing very nitpicky development, like making matched color separation negatives.

Drew, Trask's issues appeared when demineralized water was used, but not in tap water. That's why this issue is non-trivial.

Yes, but I don't think it's logical that distilled water would change development that drastically. I agree with others that there must be a mistake in the preparation and change the of water is mostly coincidental to the extreme difference in development.