With firmware 5.20 and 5.30 of Forerunner 245 music, I have had issues recently with courses. I have successfully used courses and navigation in the past many times.
Recently, maybe starting with firmware 5.20 or Connect app update (unclear), when I was loading a new course into my watch, a different course was in fact displayed and tracked! I've had the issue twice, with different courses.
It seems to be worse for courses with long-ish names "Lange Geer 32 k" vs "Lange Geer 32 k big loop".
To get rid of the issue I deleted all the loaded courses, and then uploaded only the one course, and the issue was reproduced.
This is quite clearly a bug with a minimal working example. Please fix!