I have found that version 1.31 was the last stable release for the X3 as it fixed the hanging issue in version 1.23. Version 2.1 is mostly a disaster. My unit couldn’t play three songs without locking up and you need a paperclip to reset it. Being that nothing has come out of FiiO to support the X3 since version 2.1 in December of last year and they stopped responding to emails, I’m not expecting further support for the X3. I think they are focusing on the X5.
They already announced (*not here, but at their own forum) a new firmware release planned at the end of March / early April. The reason it takes so long is because they are redesigning a lot of the UI / improving the code so it will be fairly major upgrade.
On the other hand, 2.1 has been quite stable on my X3. It is far more stable than the older version.