I agree that is somewhat remarkable, but actually there is a logical explanation.
That time interval is about 2^64 seconds.
Now, in 64-bit two's compliment binary arithmetic, if you start with an a small negative number -x, and treat it as an unsigned int, you get 2^64-x.
So what actually happened is that the start time for the attempt was after the stop time, which is, of course, impossible - and Moodle's format_time function must produce weird results like this when given a negative time.
So, how did the start time before stop time situation arise?
Do you, by any chance, use several load-balanced web servers? And if so, are their clocks properly synchronised?