I only do enlarging for lith, other than some inkjet negs to lith , but my main workflow is with an enlarger so I cannot comment on your working method.
I started using Champion Nova Lith A B -- If I could find it again I would stick with it.
I currently use fotospeed AB,, I also have used Morechs 5 which btw was really good.
I just saw the Arista A B in larger liguid containers and may give that a go.
If you are every bringing tongs backwards from stop to developer it does not matter what developer you are using you will get contamination.. I would advise you
to get out of that practice.
the pull time for Ilford WT is very different from other papers and I think this may be giving you some problem... I would use another recommended paper, until
you solve your problem... most papers you pull the print when the image looks right in the developer... That is not the case with Ilford warmtone as all the contrast
happens in the fix... if you wait until the print looks good in dev with this paper , you go to the fix and the print immediately darkens and becomes useless.. very tricky.
So I would switch to a paper like slavich 4 which is cheap and works very well for lith , and the snatch/pull time is indeed in the developer.
This will start taking out variables that may be giving you grief. but as I have said I have never printed collodion images so my advice is only geared to silver and inkjet negs.