I’m still pretty sure the nozzle isn’t getting installed right. It’s a fairly tedious process to do it right. If not done right, a gap appears once things heat up. That gap gets filled with plastic. The plastic is then trapped in the hottest part of your printer. When your nozzle heats up from ambient, that section far exceeds the target heat, which glazes the filament to where it no longer can become liquid. It’s now permanently obstructing the flow of filament that goes through.
Tear the hot end down completely, clean it out, completely, and install the nozzle correctly in stages of heat.
This is a pretty good write-up on the procedure: Howto: Change Hexagon hotend nozzle - General / Hardware - LulzBot