Thank you to anyone who dove into this issue!!!
I continued to work in earnest and was just now rewarded for my perseverance. I found by deleting one of the three relationships from Regions > Region Country, the one that connected to Export > Flight Domicile, everything reappeared. I'm not sure why this caused the problem in the first place, but I'll take it, whatever it is.
Again, I really appreciate anyone who promptly started working on this question.
Thank you arvindgarg!!! That is very helpful. I've tried to ensure that the data joins matched in all cases, but apparently something is off there.