Thanks Matthew for the detailed response. I’m trying a couple of things this time (probably shouldn’t change more than one variable at a time, but we’ll see.)
1) I’ve increased my knead time in the Ank–the videos say you can’t overdo it so this seems pretty safe.
2) I’m adding a second fold to the bulk rise process, in hopes of increasing dough strength further.
3) I plan to shorten the bulk rise slightly in favor of the final proof.
I checked my yeast (young and fresh), flour (properly stored and the correct flour), used two scales to double check measures, used filtered water (have been doing that all along), and made sure porridge was at room temp. Fingers crossed. Thanks again.