Migration punBB -> phpBB3 3.0.14 -> phpBB3 3.3.12

[Ju@n]

Hi
My name is Juan, I've been trying to migrate a very very old forum, I've mostly successfully achieved that.
The original forum is punBB (which has been dead for several years now), I was able to correctly migrate it to phpBB3 3.0.14, and then to 3.3.12.
However after doing most of the work, I just noticed the passwords for the users don't work after the migration, what is curious is as I still have 3.0.14 "alive" I tested the login for a known user/pass combo and it works, it won't work on 3.3.12.
Even though the DB for both phpbb instances is the same (I know I shouldn't use 3.0.14 with an "updated" db, but as I was diagnosing I didn't mind testing)
Not sure what's happening that 3.0.14 is able to correctly login whereas 3.3.12 is not using the same values.
The passwords on the DB start with $CP$, not sure if that's helpful or not.
Let me know what other information you'd like

What version of phpBB are you using? phpBB 3.3.12
What is your board's URL? Private still
Who do you host your board with? Hostgator
How did you install your board? I used the download package from phpBB.com
What is the most recent action performed on your board? Upgrade from 3.0.14
Is registration required to reproduce this issue? Yes
Do you have any MODs installed? No
Do you have any extensions installed? No
What extensions do you have installed? VigLink
What language(s) is your board currently using? en_us
Which database type/version are you using? MariaDB
What is your level of experience? New to PHP and phpBB
What actions did you take (updating your board; installing a MOD, style or extension; etc.) prior to this problem becoming noticeable? Basically what is described up top