While I have never experienced the shift to a lavender color I can agree that may well be an early sign of exhaustion, hard to believe the vessel is at fault, rather the vessel maybe somehow contaminated
I mix the Sol. A and store in a 1000ml bottle and store for most times 4-6 months, never have I seen a shift away from clear solution.
When the bottle does get around 1/3 full and I have a large amount of film to D from an extended trip I would mix another 1 liter and combine the two and work from that same stock solution knowing that each A & B solutions would extend through the D of the entire run of film.
I still use the original PyroCat HD, have tried the two bath scenario with low density results but do plan on tweaking that technique through trials to take advantage of shorter D times.