Any chance you travel between San Diego / Tijuana? I've had no problems for ten years and suddenly in November, I've been dealing with this annoying "feature" daily. Sometimes I get the message you posted, sometimes not. I've spent 20 hours on the phone with T-Mobile customer support who often ask the same questions and run me through the same troubleshooting steps - to no avail. I once was transferred to an Apple tech specialist through T-mobile. He was super ***** from the start and told me that Apple wasn't capable of turning off an esim through the phone. He said, "If that were possible, we'd be receiving a lot of calls about it." I keep telling T-mobile, "I just want the esims to stay on."
Hope we find a solution soon.