Is it possible to fix this so players know it's a possible origin point/lore reasons?
This is actually at least the second time in a few years Hawaii became a point of in-game contention between characters (I will bet money this came out of arguing about pineapple on pizza), and I do remember there being some kind of reason back then that people thought it had ceased to exist but whether that was based on a plot or someone writing ad hoc canon in the moment based on the 2101 map, I can't remember now.
So when I do end up talking about outside the dome, and it always happens, I try and keep the macro bits vague and put my details in on the micro level.
What is Las Vegas like? Just another sprawl chum. Corps and dregs, rich and poor. You see one city you've seen them all.
What was my home like? A tiny two bedroom apartment with holes in the walls, a leaky roof and flaky pink paint. I remember this broken pipe poking out of one wall. I almost died when I impaled myself on it when I was ten and tripped on the torn carpet.
The more micro it is the more I can make definitive statements about it without getting push back from others. The more macro it is, the more likely it is that someone will push back.
And when the push back happens, I tend to just wave it off. If I had a character with an approved history that says they are from the Hawaiian Islands, then my character knows and believes that this is true. If someone else claims they don't exist then I would have my PC wave it off. "Whatever. Think what you want chum."
Also keep in mind that PCs are not a great source of facts in many aspects. One, because most of us don't know the facts, even if some of us decide to act like they do anyways. If some IC character claims there is no Hawaii, then that's that. That PC either believes it or is messing with me and/or others. It is not a statement of fact about anything. At most it's a statement of what they believe to be true. This can even be the case if it was an NPC saying it as they can also lie and be uninformed.
Finally, as I believe I have seen some of what you describe, I just want to say that the people behind the PCs may not be objecting to things as much as you think. Or trying to define the IC truth for everyone as such. One character's comments sound like a person RPing a lack of education. Another character's comments seem to be an attempt to slander. Other comments might honestly be PCs doing what people in real life often do: making declarations of fact when they don't know something.
I wouldn't take any of it as someone trying to define the truth of the Sindome world as in almost every single case, none of them CAN. It's beyond them. And nobody needs their approval to play on with their PC using their approved history. Except for staff of course and even then only as staff and not as NPCs.
The 2101 map is also at least a little non-canon because Portland was destroyed in the timeline (raise your hand if you also forgot about this and referenced it all the time).
The timeline also states that in 2054 the sea levels are 50 higher than in 1995. Using a steady progression for simplicity, sea levels would have been about 41.5 feet above 1995 levels already before tidal walls were conducted in places not already specifically called out. That's a very different cost line.
Regarding Portland, I've always imagined the southern part of the Vancouver/Seattle/Portland sprawl where Portland is today as a mix of ruins and new urban growth. It was destroyed about 90 years before the game's present day and many characters have had approved histories with them coming from Portland (some of my own even) so I figure the map can't be all wrong.
But the fact that two people can read the timeline and map so differently is why I think this lore article might be useful.
