It was either:
Sex and dope and dereliction of duty among the crew.
Or
Dope and sex and dereliction of duty among the crew.
Both or a mass orgy with drugged crew with capt. sleeping it off. Why, what could be a better place to hold such a ship-wide event than in a crowded busy shipping lane?
Another take is that the radars and other forms of ranging did not work or were off-line for maintenance.