You know what I just realized, that original article I said I was following said to bleach before proceeding to develop normally. So even though I washed for about 10 minutes after the bleach, I'm sure a small amount got into the dev. So I'm going with that as the cause
I think the article said to develop a slide film in B&W developer then beach it, was and re-dev in C41.
Missing the initial B&W developer will mean that no silver reduction will take place, so when the blix* goes in it will remove all the silver leaving the film blank.
The process should be:
B&W development to make all exposed silver develop.
Bleach to make unexposed and undeveloped silver soluble.
Wash to remove bleach and and a small amount of unexposed silver.
C41 development to make the developed silver reduce further.
Fix to remove silver made soluble by the bleach.
*N.B Blix (beach and fix combined) and normal colour (EDTA) bleach are not interchangeable in the above process–you'll end up with blank film with no edge markings! Using fixer before development will do that!