this has coincided with a particular signature campaign being managed by a particular campaign manager who was vouching for a neutral trust to be removed from a participant but I will not claim that is the only reason I am receiving PMs, I think the timing is suspect that is all. It also has coincided with me removing or revisiting other neutral trust recently.
If you are already reviewing other trust feedbacks you've left, then there's nothing to draw up about the timing of the request. It likely has nothing to do with what whatever campaign manager vouched for, nor does it really matter.
If you left a 'negative' neutral feedback, then it's not surprise the said accounts are acting dubiously as you said, that could be one of the reasons they got the feedbacks in the first place. A neutral feedback does not limit one from much on the forum, so they would not be losing out at all, and maybe they don't know how the forum worse really.
I leave a couple of feedbacks, few and far between, but have only been contacted to remove a negative feedback I left. A request which I declined by the way. It's best to give feedbacks within the limit you can manage and review periodically.