***UPDATE***
So.... this fix only worked briefly and then I encountered the issue again. I read in another forum that removing KSP from your steam library could be a possible fix (for a different problem also related to sound in the game), so I tried that, played for about an hour and encountered no sound loss whilst switching from Map->Craft & back again, over and over, etc. This could be a potential solution but I'll have to let you know when I have more time to confirm.
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Hi Everyone. So, here is what fixed the sound issue for me; (running waterfall mod)(Running most up to date version of KSP)
Remove the "sounds" folder from the "Waterfall" folder in your "Game Data" folder or wherever you store your mods. Now when I toggle the map and toggle back to my vessel, the sound is...there! it SOUNDS! It doesn't appear to negatively affect any other aspect of the mod but if someone wants to do a deep dive to see if that is indeed true, please let me know.
Hope this helps! I can't tell you how happy I am to be hearing my jet engines again!
