AP has a valid idea here, but I still am convinced that if the bait cavities stood vertically instead of angled in the mold the issue would not exist. I think that as plastic goes into the cavities the small areas of restriction between the body segments is where the air is getting trapped within each segment. There isn't a lot of plastic in the segments and it will cool in a blink so any air caught in there is a dimple. There is no venting to void air in what is the top of those segments behind the restricted areas as that "waist is lower than the top of the inside of the segment....at least that is how I see it. I think that the intermittent full filling happens when things are "super right" and that air is voided during the injection, but this would also include having an injector that is fully sealing as per AP's observation.
As I mentioned before, I have one mold that balked a bit occasionally yet the other couple are clean injectors and all molds are shot clamped together one right after the other and only the one has ever been iffy, but is no longer with a little air relief help. I haven't touched an o-ring in my primary injector ever so I don't feel that it has been a part of it at all. That's not to say that X2 hasn't got a minor air issue in his. My primary injector is NOT a Do-It injector, however my twin injector is and I had an o-ring issue in one of the cylinders of it not all that long ago that was letting air into cavities and re-ringing it took care of the problem. Rather than dimples the problem I encountered was that the good cylinder would force an air lock on the bad cylinder so colors would not flow properly.
These things can get challenging to sort out, but they're also frustrating for everyone too, especially the crew making the molds. The crew in the shop are top notch....they'll get it figured out.
