1. If your contract is for 3 years and you resign before that time then officially you are breaking the terms of your contract. You should contact the labour department to see if there's a way to resolve that since you had renegotiated the time period.
2. My understanding is that the UAE labour ban
applies when changing sponsors so if an employee remains in the same UAE free zone
but with a different employer, then the sponsor doesn't change so a ban doesn't apply.
3. If you find another job in JAFZ
then there shouldn't be a labour ban since your sponsor won't change. The JAFZA labour office (or equivalent) should be able to clarify that for you.
4. Employers and sponsors don't implement labour or visa bans in the UAE, the UAE Ministry of Labour
and Immigration Departments do that. A sponsor or employer can request a ban as far as I know but I don't think they can instruct the relevant authorities to impose a ban. That's why it's probably a good idea to file a complaint with the labour department if an employer is out of order. There is at least something recorded if an employer later tries to request a ban.