I made a discovery last night that has put to an end, virtually in one day, about a month of plateau. If you have an uneven growth from mewing i.e. ramus lengths differ, more exposed submental muscles on one side, then the solution is a little counterintuitive.
Your intuition might tell you to apply greater force with your tongue on the side that is less developed, but you should actually do the OPPOSITE, and youll feel more pressure in your skull doing so. I saw more change since ive discovered this than for a month prior. Id love to understand the mechanics of whats going on, but I'm posting this from my phone and it's kind fo awkward posting as it is.
You were straining one side of your face by pushing harder on that side, so more than likely you were accidentally recruiting surrounding muscle groups.
My solution (it's not for everyone) is relax my left zygomaticus which was overly tense (it pushed the left canine in). Everyone has asymmetry for different reasons.
long term that is a bad idea, you should be trying to apply force symmetrically with your tongue central to the best of your abilities. Pushing harder will result in different asymmetries that you will later have to fix. now one side might get more pressure as a result of pushing symmetrically but that is to be expected. if your tongue isn't central it won't work though.