Could be a while until I get to trying your fix, but I will keep it in mind. I have a fuji roller processor, and was printing ra-4 on old royal paper last postcard exchange. Winding off 30 prints, the last ten came out progressively more magenta/purple, paricularly on some where there was known edge fogging.
So I peeled the processor cover off to check the dev tank temp, and whoa, the thing was up to 45C.
Turns out I think I now have a flakey set point potentioneter or intermittent solution temperature thermistor.
I swapped all of the electrolytic caps out of the control board three years ago, so they should not be a problem again yet.
So yes, even regular RA-4 can go purple if over developed. I will try a more dilute RA-4 for the portra mono stuff next time I have the zing to use it.