Before I get onto cross curve I will also ask you, do you have a proper voltage stabalizer on your colour enlarger? if not this will cause you these kinds of problems.
Very Basic Cross Curve Description
When I use to make internegs from slides years ago we were always balancing the film out for cross curve problems, basically the problem is where complimentary colours, green magenta, yellow blue, red cyan, would be present in either the highlights or the shawdow areas of the balanced print and we would adjust the colour and exposure at the interneg stage to correct for this. { we would use a graduated grey background from pure white to black and on some point we would see the cross curve (rainbow) and this would then have to be filtered out.
Please take note this was a specific problem with transparancy-interneg-print problem and was *not* something that we would look for with camera neg-print.

I do not think this is the problem you are having, I really think it is a mechanical , dicroic , voltage or chemical problem.

I was always taught to always move the dichroic dials to my new setting in the same direction every time. these dials are mechanical and with age become a bit wonky. so its something like the old dial locks we used in highschool, unless you came from the right direction each time you would never open the lock. the same is true for Colour manual enlargers, if you do not dial from the same directon you will have trouble getting consistant colour. If you check you will notice some play on the dial or a soft spot , at least I have noticed this with every colour enlarger I have used .