CK II - Black Flags for newly created Dynasties, Holdings

[BruceWayne]

One line summary of your issue
Black Flags for newly created Dynasties, Holdings

Game Version
3.0

What expansions do you have installed?
Jade Dragon,
Monks & Mystics,
The Reapers Due,
Conclave,
Horse Lords,
Way of Life,
Charlemagne,
Rajas of India,
Sons of Abraham,
The Old Gods,
The Republic,
Legacy of Rome,
Sword of Islam,
Holy Fury, All of the above

Do you have mods enabled?
No

Please explain your issue is in as much detail as possible.
Every new dynasty or newly created holding will have a black flag, instead of a randomly generated one. I'm not entirely sure, but it seems affect some existing ones as well.
As far as I can tell this only affects Catholic Christians, then again, this might happen to other faiths that use the shield shaped dynasty sigils.

Steps to reproduce the issue.
Build a new holding in the HRE as a Catholic -> Holding has black shield
Bastard/Cadet branches in catholic dynasties -> black shield

There is a small chance that random courtiers/holdings will get black shields as well. For the holdings, it mostly happens to cities/bishoprics -> It appears that these are the non-defined flags that would be generated on game start

EDIT:
After taking a closer look at the flags in the Flag Editor (wasn't available to my character before), it appears that all black flags have a non-existent symbol applied to them. It shows something like 34/31 or something to that effect. I do have all relevant DLC though, so I think that's the bug right there.

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