Not 100% sure of this is a bug, but it’s weird indeed.
I got this warning message today, but, unlike other times, there are no O2 signs anywhere to be seen.
Also I don’t know if it’s relevant, but my average RDI is 2.
I’m using a galaxy note8, android 9, and a ticwatch pro 3. The program version is 20210808 (22471) Premium