cmi.core.session_time is a scorm variable, it’s not related to any course internal action or timer. It counts the time a user spends in the course, i.e. the time the window is opened. When the window is closed its value is added to cmi.core.total_time that informs you about the time the user has taken from “not attempted” to “completed”.
So, one of the first things that should happen when the course is launched would be to (re-)set the session time variable to “00:00:00.0”, before it starts counting. The error says it cannot do that. When you go to the next page the course tries again and the error is repeated.
“Not initialized (301) Indicates that an API call was made before the call to LMSInitialize.”
Seems like the connection to the LMS is missing, maybe due to a missing internet connection.