I think that entware and entware-ng are not fully compatible each-other, I think that I've read something about that. Entware-ng is the "last" entware, I think.

But I don't think entware-ng and optware in the same system can survive, I don't know exactly but, I think that use the same path /opt!

So, try to
1. Disable entware
2. Disable entware-ng
3. Reboot the nas
4. Try to reinstall jd2

Alternatively if you can install the container station, I know that exist one container with jd2