RA developer should last over a month with no degradation in the image. When it does start to go bad, contrast and dmax go down. You don't get off color white areas.

There is sulfite in the developer to prevent oxidized color developer from having that effect.

I would expect that your problem is from bad stop bath, no stop bath, bad blixing or fog.

The stop should be mixed according to the manufacturers recommendation which I think is about 1% or 2% acetic acid.