I have seen that the user Garmin-Sierra posted in various threads this:
"Software version 15.19 has been made available, so anyone who syncs through Garmin Express should now be able to update their unit to that version. If you would like to enroll in our Beta Software program, you will need to update to 15.19 first, and then follow the steps in Enrolling in and Learning About Garmin Beta Software Program.
If you are still unable to update your watch, please start a new thread."
And then closed the comments.
I´ve just tried this solution but nothing happened, my 955 is still stucked in 13.23. Please do not confuse us, the problem is not resolved. That´s why I am starting this as a new topic.
Garmin Team, please find the solution