Turns out it all starts with this “read binding table” code that sends the binding request. I have these lines in my custom driver too but I’ve just realized they are not needed for new devices like RODRET and other modern buttons, that’s why the new buttons work fine even with the response to that binding request failing.
But those are needed for old buttons, the ones supported by stock drivers like the TRADFRI 5-button remote. At least for old firmwares that had this weird binding procedure.
New firmwares for TRADFRI buttons like 24.x do not require that type of binding for them to work and send the events. Maybe it would be nice that SmartThings could update them, although not automatically by default or it would break a lot of things for existing users.