[King Custard]

My ideas are very similar to yours - as in grab another grip and customise it.

My opinion though is to keep shooting the new grip for a little longer paying particular attention to hand position.
It may well be that ou need to adopt a different hand position with the nexus grip...that previously or now there is a different amount of torque being induced on the release.

I would suggest waiting (ha) for a wind free (or less windy) day...and shooting without stabilisation to mask any torque effect ..shoot and scope 2 & 1/2 dozen- measuring the group sizes with a tape measure....
then change grips - and do the same again. Alternating grips and finding the right position for your hand on the new grip. (I've found this ain't always easy nor quick)

I've personally questioned the nexus grip for 'ease of consistent hand position'...but found it was myself rather than the grip that was at fault.

My guess is that your bow hand and grip will become more of a 'unit' the more you shoot.....but of course, a change to a grip shape that you are used to may shrink groups pronto.