Staining on Negatives

I seem to always be finding new ways to screw up my process. I processed 6 sheets of 4x5 HP5 the other night and noticed yesterday that there are yellow stains on 3 of them. Developer is HC-110 dilution B, Fixer is Ilford Rapid Fix, and stop bath just a rinse. Same (basic) process I've been using for a long time with no ill results. What did I screw up? Time, temperature, rinse, phase of the moon? Aggravated!

Oh, and I'm using the same crappy FR tank I always use. I hate the uneven development I get with it - I've gotten better with it but still get marks in the sky. Before I plunk down $85, any thoughts on whether I'll be better off with the HP Combi tank - I have no intention of processing film in the dark so no interest in tray developing (that's why I use paper or Arista Ortho-Lith for 8x10).

Thanks,
Dan

It's dichroic fogging. I use HP5 in 5x4 as well with no issue, try a double rinse or proper stop-bath & plenty of agitation at the start of the fixer stage. It can be caused by dev/fix mixing and the development continuing slightly.

Ian