Has anyone experienced Japanese staff speaking overly casual when they see you’re a foreigner?

I’ve been living in Japan for over 10 years and speak Japanese fluently. I work at a Japanese company and handle everything in Japanese without issues.

But sometimes in stores, restaurants, or service counters, when staff realize I’m a foreigner, their tone suddenly becomes very casual — almost like they switch from polite customer language (敬語) to tameguchi. It’s subtle, but noticeable.
It doesn’t happen all the time, and I know most people don’t mean anything bad by it. Still, I sometimes wonder:

Do they assume foreigners don’t understand keigo?
Are they trying to be “friendly”?
Or is it unconscious bias?

Has anyone else experienced this? Especially long-term residents who speak fluent Japanese?

I’m curious if this is common or if I’m just overthinking it.