I understand the flushing concept and I like it - a lot. But, you are not flushing that middle cavity.
The molds that worked, the lures look a lot thinner and they are all connected to a flushing vent. Perhaps the flushing reservoir(s) need to be increased, by extending with another pipe. You can then extend the flushing until you get it right. Finally trim the pipe to the length that works, so it acts as a guide.
Something else to consider; the plastic takes the route of least resistance. You need to give the plastic a reason to flow through that middle cavity.
The point of your thread was to share your method, which I don't recall seeing before, so well done for coming up with an original idea and putting it into practice, and good on you for sharing. But, if you show a problem, we all want to help you fix it
Dave