When I was traveling all over for work, I had issues with EU countries, Canada, Mexico, and China.
Canada was the worst. I ended up getting sent back to Buffalo, (then rented a car and drove across the border to Toronto, but still)
Going to Scotland I ended up stuck at Heathrow for 24 hours. All of it was paperwork non sense.
The kpop group sounds like they tried pulling the tourist excuse, and then answered wrong when they said they were working. Or like going to Canada for "just meetings" means you don't need a work visa.
And if you try and get a work visa, it better be to train canadians to do the work, and not actually doing work that a Canadian could do...
The British Muslim's, sounds like it's a case of one family member may have something questionable, so they hosed all 11 of them, including the children, which is ridiculous. The Airline/list should have at worst detained the 1, and then investigated more thoroughly to see if it was a valid reason to prevent him/her from coming over. Not kept the kids and rest of the family out.
The entire security theater mixed with customs/immigrations for all countries is ridiculous.