Yellow Mystery

I've been working with ILFORD's direct-positive fibre papers in my 4x5 Harman-Titan pinhole camera.
After processing a batch of paper negatives some came out normal and some with a terrible yellow cast.
Does anyone out there know what is happening to my paper negs?
Process one will be fine ... the other yellowed.
Any thoughts?

you might want to edit your title to make the problem clearer, might attract more attention

Did you process the entire batch at one time in a tray, or separately? If all in one batch, improper agitation could have caused some prints to not receive adequate development, for example if some prints stuck to one another and didn't get fresh chemistry throughout the process. The same for fixing.

Also, too many prints through the same developer could have caused exhaustion. Same with inadequate or partially exhausted fixer.

Lastly is the rinse. I've noticed that properly processed Harman DPP will appear slightly pinkish in the highlights when first out of the fixer, but a good rinse clears it away. But I haven't seen yellowing.

~Joe

Are the exposure times about the same for both batches? Just wondering if a really long exposure might cause your issue. Does selenium toning the prints take away the yellow?