1 Fake positivity
2 Co-workers that are "happy" to work during PTOs
The first one is described in the article. The second one is somewhat related to the first one or could even be the result of fake positivity. Working during a paid time off (PTO) is terrible for culture – makes your co-workers feel guilty if they won't spend a few hours at work during their PTO. I almost feel like an employee's access to Slack/E-mail should be restricted to read-only while they are on vacation.
If you are one of those two, stop kissing your manager's ass! Enjoy your vacation–forget about work.