Overuse doesn't cause problems. Misuse doesn't cause too many problems. Combine the two . . . Some pianists can practice six to ten hours with no fatigue while others can acquire cramps in seconds. What is different is improper and proper movement.
Technical issues can't always be seen. Especially if your teacher is looking at your hands. That would be like looking at the hood to figure out what is wrong with your car's engine. The hands are the result of the work of the arms. You teacher should also be able to hear technical issues and from asking what you feel. If your teacher "lost a leg in the war" they will be able to hear lack of rotation, abduction issues, twists and needed forearm adjustments. If your teacher doesn't know what those corrections sound like then they won't know what to listen for or what the difference sounds like. For instance, a missed note doesn't necessarily mean you need strength or more practice, it could be because you need to readjust something. You can't see those.
Also, I am of the opinion that injuries are forever. Sure, they heal but the torn fibers of tendons may always have a weakness at the site of repair and will be much more susceptible to future injury. You can break a fishing pole in half then tape it back together and it will work but not like it used to. If your pain is due to tendon inflammation, micro tears, scar tissue or adherence, those can take two months to two years to heal. The key is to stop doing what causes the inflammation and that is not necessarily "rest" but simply moving properly and discontinue using the tendon fibers that are currently compromised.
Finding the specific fibers can be a challenge and your teacher's ears and your verbal feedback about what you feel and when, will reveal all. A good deep tissue myofascial massage therapist might be able to feel scar tissue and nodules but still, it is a lot of detective work.
You need to understand how tendons are made. They are sort of like speaker wire. Cut one wire and inside there may be three bundles of wire and within each bundle, several more wires. Your muscles are made up of hundreds of fibers which are bundled in fascia tissue. Then another hundred are bundled. Then hundreds of these bundles are bundled. Then hundreds of those bundled bundles are bundled to eventually form a muscle. All those bundles merge down into one huge compacted bundle which becomes our tendon. Flex your muscle, it pulls your tendon and your tendon moves your finger bone. Your fingers have no muscle of their own.
If you have ever played with your fingers, you may discover that you can move them at each phalanx. A finger is capable of thousands of positions but it is not necessarily just a tendon or muscle problem but, your pain can because there are specific fibers or bundles which are scarred or are adhering to one another causing dull or sharp pains. Finding the bundle or movement which is causing the problem is the key. It may not just be a flexor problem but the flexor combined with an abductor or something.
I was once paralyzed with pain and as long as I moved properly, I was pain free. I don't feel I am "healed" and that the pain can come roaring back if I ever move improperly again. Because of this, my teacher forbid me to play old repertoire because my old improper movement that is hardwired into muscle memory is too powerful and too easy to let out of the cage.
And another thing, just because your teacher says they can work on technique doesn't mean they can. Every massage therapist says they can perform deep tissue myofascial massage but they can't. They can go through the motions and understand the concept but a trained therapist in trigger point release and fascial tissue massage will know what everything should feel like and, not just an arm or a muscle but, those aforementioned bundles.
Remember dissecting frogs in biology class? Welp, your arm looks exactly the same. If you live near NYC, there are dozens of teachers there who work specifically with injured pianists.
Technique is knowledge and science. There is nothing mystical, talent based or hocus pocus about it. My car and cell phone are science but to someone from the 18th century, IT'S WITCHCRAFT. BURN HIM.
Many teachers may disagree but, they're just not injured yet.