So just to give a quick update on how this went:

Since pfSense 24.03 is based on FreeBSD 15 I proceeded with a FreeBSD 15 installation on XCP-ng to see if the issue stemmed from there. FreeBSD15 installed and booted correctly.
From there I ended up testing the development snapshot 24.08.
Also installed correctly and booted.

So whatever issue was there between pfSense 24.03 and XCP-ng that was preventing it from booting, was only present on version 24.03.

@olivierlambert I changed the memory settings like this

I'm going to proceed with the upgrade and post the outcome

@high-voltages I believe turbo boost takes it up to 3.3GHz. The 2.7 is reduced workload

Alright I updated XO again and the problem is gone.
I would just like to comment that unlike described by another user that was only happening on single-node installs, this was happening to me in 2 out 4 nodes in a cluster. Two hosts would show normal, and another two showed glitched.

Anyway, SOLVED!

Well since there is no issue when looking at XOA but only on XO, I am going to disregard this issue and wait to see if it resolves by itself until the weekend and if not I'll try and remove this XO build and make a new one.

Thank you for your suggestions, I'll try and let know how it went.