Sounds like the adapter isn't allowing the action to close completely causing shallow latch engagement, insufficient engagement will cause pop-opens. You may have to modify the adapter "rim" so it seats deeper in the chamber rim cut. It may also just be too big for the chamber and the body of the adapter needs to be slightly smaller, you can check by covering it with ink from a black marker, or even smoking it with a candle, then chamber and remove it, any marking that's been removed shows where it may be too big for the chamber and is binding.
The ejector to extractor modification that you can do by modifying the ejector only keeps it from ejecting, it won't increase the ejector's capability to remove a hull or in this case, the adapter, it's still spring powered. A factory extractor is mechanical, doesn't rely on a spring and is much stronger. You might try the ejector tune(FAQs) to increase spring tension.
Tim