May try putting something under the vent-end so it's at an angle.
My theory behind this- I believe that, at an angle, the "lower" details in the cavities should fill 1st as the plastic flows, leaving the "upper" details to fill-out secondly which should be successful if those details are vented. Plastic moving upwards shouldn't (again, in theory) clog vents before the cavity is filled, if the molds' details are given time to process everything. Complex, numerous, small details like to trap air so we may need to work harder to overcome those air-trapping tendencies.
Why it's now acting up is a head-scratcher.