I feel out of the loop. Not sure if it's me just getting old or not understanding social nuances, but this all feels like people drawing lines and taking sides on something that's going to vary based on cultural background, age of peers, personal experiences and idiosyncrasies, etc. I don't feel like it's a good situation to have two (or more) sides each claiming that it's offensive to them if someone who doesn't know them responds using a different side's preferred response. Kinda puts customer service workers in an impossible situation.

I reflexively say "thanks" when another human does something for me, and I don't particularly care what their habituated response is. Especially for people working customer service, who are just getting through their day and running their script. Mostly people echo the response that they're used to hearing from others, so unless I have some reason to think they're being snarky...??? Your noncommittal phrase of thanks received a noncommittal response, and both parties can move on from the exchange and do something else with their time and energy.