As someone who upgraded from an OG Xbox to a series X, I can say that the loading screens are hardware related a vast majority of the time.
But there is also a legit bug where the game simply doesn't let you off the black screen for inexplicable reasons, and yes it is usually during combat.
My entire crew has experienced the bug and we are all in different types of systems, so it isn't hardware.
But the "flow" is generally the same. Get killed. Go to ferry. Door opens. Go through door. Get green pinwheel at the bottom.
Notably, the ship is NOT sunk and you are no longer in the ferry area. While staring at a black screen/green ship wheel, you can hear combat. Bucketing. Repairing. Remain crew begging for help because they are undermanned. And you are loaded in "enough" that you are moving/attached to the ship model as you experience thus even as a ship is in motion. They aren't sailing away from you leaving you to eventually hear waves. You just get to listen to chaos.
I've had this persist for 5+ minutes. Sometimes the ship sinks and that's when the game spawns me in to just take a mermaid. Sometimes the ship gets out of combat and I spawn in when things are calm enough for the system to catch up. And sometimes, for no rhyme or reason, after minutes of waiting, it just decides "okay, now I can load you" and I pop into existing in the ongoing combat.
There is literally no easily discernable pattern beyond "usually in combat" to explain this issue. And being in a series X, I can say that loading into a brand new game, where the game has to load the entire world, is still faster. New game = 15 seconds from setting sail to tavern wake. And 2ish "loading panels" artwork in between. Pinwheel of death, many multiples of minutes.
This isn't a hard drive or memory bandwidth issue. When it happens, it has every appearance of a server-side issue of being under too much strain and not having time to sent the client acknowledgement that you are loaded in and "releasing" control to the player. And even if it only happens 1 time out of 100 to lose a battle or lose progress to it is one of the worst player experiences to have.
The OP is right. This needs to be fixed once and for all. And not just for solo reasons.