@Bryanvh Looking at the code, I saw that an exchange was taking place via this certificate.
So when you told me that the master certificate was missing, I tried to put myself in the same situation as you (by removing the certificate) and trying to join the pool.
Having encountered the same error as you, I determined that running these commands fixed the problem.
Indeed, I think the upgrade from 8.2 to 8.3 is the cause. To be more precise, a change occurred in the XAPI during the certificate exchange in version 8.2, and I think it's possible that your 8.2 host wasn't up to date when it upgraded to 8.3 (I'm not sure).
In any case, I'm glad your problem is solved.