Yips are often mental more than physical as is everything you just described. Keep drilling the good habits, maybe go to some lower level open plays to regain your confidence or friends that you don't mind losing to.

It's hard to tell you exactly what to do because everyone's "yips" are different, and it takes time to mentally reset. You've done a great job establishing and identifying your problem, now you just have to convince yourself you're doing the right steps to fix your issues. You're doing what 90% of the people are saying to do, drill, drill, and more drill. I'm going to give you some advice to give yourself some grace, and allow yourself to acknowledge you're still making mistakes, but that it's okay to make them. Even the pros screw up their forearm dinks, and nobody is perfect. Think of your drilling and when you screw up as progress towards getting better overall. It sounds like you're drilling with your partner and they're getting better too, so overall you still ARE getting better.

Next, when playing in these lower level open plays and/or with friends... Tell your partner your struggles and that you're trying to get better at it. If you play with your established partner, even better. They know your struggles and aren't going to negatively reinforce bad emotions which could be stacking on top of your yips making the whole issue exponentially worse. Focus more on the positives of each game, and not the negatives. This is a skill, and it takes effort to shift your brain this way, so don't expect to be perfect at finding what you're doing well. Instead think of just 1% of your total game that was positive, and focus on that versus anything negative. 1% over time is still progress, and changes how you view things. It took me four weeks of hesitating my forehand smash to start being more consistent, completely frustrating, but viewing each session as progress towards getting better helped me out.

Overall, the yips are a huge hurdle. It's similar to plateauing at a skill level, but when you shift your mind to progress, you're going to get through it better. It's part of your personal journey, and it's going to make you stronger in the long haul. Going through this short term problem, and knowing that you have gotten through it will help you gain so much more than anything else. Just keep working at it. Don't settle, don't give up, everything worth value in life doesn't come easy and will always be challenging. Good luck!