What does the asterisk at the end of the timestamp in the ULS log mean? Does this mean that this event has occurred multiple times?
That is normally the line continuation character and is used whenever a particular message is too long to be included on a single line. I can't say I've ever seen it used quite like is in the picture though.
According to this, it means :
A trace log message can have multiple "middle" sections. Trace log messages are not guaranteed to appear consecutively within the trace log. However, the "middle" and "end" messages contain an asterisk beside the timestamp in the trace log. Developers can use the presence of this asterisk to identify whether a line is a continuation of a previous message. In addition, each line of the trace log includes the ProcessID and ThreadID, enabling a developer to follow the flow of a specific thread to see the surrounding messages.