Blue "!" on overmap - what is it?

I have a base (not basecamp) in a military bunker. Today I’ve noticed the tile where the bunker is is shown as a blue “!” instead of regular red “b”. It is not a map note (turning off map notes doesn’t remove it) but it can be turned off by turning off overlays.
So, what is it? What does it mean? Last week it wasn’t there so I guess it is some recent addition. Seems kinda pointless though because there’s no (obvious?)way to understand what the heck it actually means.

Is it a blinking, dark blue “!”? because if so, it’s an “auto-move” prompt that you declined. sometimes they just don’t disappear

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Mystery solved, thanks!