I quick trouble-shooting question for those experienced with B&W reversal processing (perhaps a bit niche but never mind - this is for making analogue positives to make Anthotypes with).
I had good initial success with a test roll of 135 and two sheets of 10x8 FP4+, using the DIY instructions posted here and on Photrio - using two strengths of Ilford Multigrade, and a H2O2/EDTA/Bicarb/Citric Acid bleach followed by a clearing bath.

I then attempted to process two further sheets of 10x8 last night - again, using Stearman SP810 daylight trays. Sadly the bleach stage appears not to have worked, and I ended up with two to all intents and purposes black sheets of film. The first developer produced good looking negatives, but the bleach failed to bleach out the highlights to any discernible extent, meaning that the clearing bath didn't do much if anything. Rexposure and second development only affected the shadows, thus producing a black sheet of film.

So the culprit was the bleach step: I'm still not exactly sure what happened, but I think for these two sheets (green leaves and bright/white flowers on a pure black background) the bleaching stage wasn't long enough. For certain negs it may be that the bleaching needs rather longer. Additionally, the bleaching time I used (9 minutes) is for continuous rotation in a Jobo tank, perhaps usually by far the easiest way of doing this, though not for sheet film. So for continuous agitation in a tray I suppose that an extra minute or so would be usual and I should try that. I've also rechecked my chemistry mix and it's fine (and has been confirmed to work already, on my first three attempts). So probably not bleached for long enough - I should inspect and persist.

I'm still not certain why an image with fewer highlights in it would take longer to bleach, but perhaps the answer is counterintuitive? Perhaps it's the case that the bleach needed to have a particularly localised effect, in the centre of the compositions?

Anyone any further ideas esp on the latter aspect? Thanks in advance.