My burner phone, with disabled wifi, bluetooth, and data, was owned this year.
These days I update, backup, and lock down my daily use iPhone before going. See my post earlier in the comments for more details on that. In terms of what was happening in the last two years at DEF CON that could get you with all the steps I took, OpenLTE networks were tricking phones into attaching to them and the most disturbing thing I saw of that was middling of TLS. However, it was of course with a self-signed certificate so as long as you didn't accept the cert, you were likely fine.
If you had an older phone and one without all the latest updates and wasn't configured to be mostly silent, then your experience could be very different. There are a surprisingly high number of SMS exploits which still work to this day on a large number of phones and of course SS7 has architectural weaknesses which will likely never be fixed.
I am sure that many folks would be very interested in seeing any supporting data/captures. This is incredibly uncommon.
Unfortunately when it comes to calling it "incredibly uncommon", we really don't have any widely deployed solutions to identify rogue cellular base stations so it's very difficult to say how often it happens IRL although the only times I've ever seen it happen have been the last two years at DEF CON.