- See here for the initial bug report. In short, some time between 2022 and today, old-style, simple submarines started to shadow the hex they're under, and also somehow hide what's behind them (like if they had the "cut LOS" special, which they haven't obviously).
I can't exactly pinpoint since when this started happening since I don't have archives of all the OG executable versions. I know that an old executable I have (file date 17/07/22, in game it says "0.93.5.0") still works as expected (no shadows, no LOS issues). The regression happened after that.
What I assume to be the latest executable (file date 09/01/24, in game it says "0.93.5.RC1.e") submarines shadow the hex they're under, and somehow hide what's behind them (like if they had the "cut LOS" special).
Test scenario, just put it in my old E-File and load it. The coastal city on the left has a radar, and you'll see an arrow-shaped shadow in the middle of the sea. That shadow is created by immobile submarines (sea mines)... You can fly the two recon planes over there to see them (the planes can see submarines, while the radar can't).
If you have an old executable available, try it again with that one and the sea will be all smooth and featureless, as expected, no arrow-shaped shadow...