Ahoy, johnlax...
Seem to recall seeing this being mentioned of occasionally occurring even in SH4..
NOT sure about in SH5 though...
In SH4, it was mentioned as I recall, of when it does, to do a quick save, quit game entirely, then reload... & that takes care of the issue... I also seem to recall iirc of a like... 1 in 100 chance for it to continue... though I can NOT swear to the 100% being recalled correctly on that aspect though... but I do know that it generally resolves the issue of Co2 build up not clearing out once surfaced.
Hopefully, this info helps...
M. M.
On retrospect, am finding that, even in SH4... the sub or boat, if you will... even though you chose to 'surface', the mechanics of it, even in calm seas... will NOT have the boat registering as having fully surfaced... a fix to that, is to then do a emergency surface... meaning blow ballast. NOT to worry, given enough time, that air used, will be replenished...
Another thing... just out of curiosity...
The previous game save before the 'demise' of your crew, did you by chance do it... while submerged.?
If so, then this would be a prime example of WHY to avoid doing saves while submerged... best time to do them, is:
1. While surfaced
2. Not near land (@ least 70 NM, if at all possible)
3. NOT near ships/harbors/sunk ships (see above # 2)
4. If at all possible, during calm seas... (doing a save during bad or seriously bad weather, will lock in that weather & reset the clock on it to the start of that type weather cycle... whether you want it to or NOT... so.. instead of having it be close to the end of it when you reload.. you'll have that bad weather extended for a full cycle more, added to the length you already dealt with it, prior to saving...
...
)
& last, but NOT least...
5. While engaged in a to the death duel, with any ship/s...
Again, hope this info helps...