It's a possible theory. Could say it depends on how bad the cart is, and how out of spec the console is. If they're a little out of spec, each, it could add up to being way out of spec when both are combined.
When you have a new car and something fails, it usually stands out in contrast to everything else working perfectly. And it's an easy diagnosis + fix for the mechanic.
But in an old car, if something starts going out of spec, it tends to get lost in the noise of other failures and wear and tear. Is the bad mileage coming from a dirty air filter? Dirty oil? Bad bearings, dirty injectors. Fixing any one of the problems may or may not be "enough" to push it back in to spec.
Could this symptom be a "poster child" for how we will observe gradual failure on 40+ year old consoles and cartridges?
In an old console, it might be bad capacitors, worn end-of-life voltage regulator, weak spring-action on the cartridge connector, marginal power-brick output, Sloppy TTL rise/fall times. It's all additive. Fixing any one of the several wear'n'tear items/problems may be "enough" to push it back in to spec.
I checked the console. Contacts are clean and all the other games work ok. Not the slightest issue. Even Pole Position from the Harmony cartridge runs ok.
Contacts are clean, are they applying enough pressure to handle any variances in thickness of the PolePosition cartridge's PCB? Just a thought, I know of no issues applying to PP.
Also, understand Harmony is rather new in comparison to a much older PP cart. The H cart is providing crisp and in-spec rise/fall times on the signals, likely enough to overcome any slop in the older console. IF that's the real problem.
Don't know what else to say other than pull out the oscilloscope and logic analyzer to dig in further, or try another PP cart!