According to a new report in the Korean media, those who have bought Samsung's 5G edition of the Galaxy S10 face a significant new issue with these devices. It seems that these phones fail to connect to 4G when the new radio bands are not available. As they have separate antennas for both kinds of mobile data, this should not be happening.
https://www.notebookcheck.net/Samsung-Galaxy-S10-5G-users-complain-that-their-phones-drop-signal-while-switching-to-4G.416396.0.html