sell side at night

This may be a noob question, but: what is happening with the sell side of LYC at night ?
Lately every night LYC's sell side reduces markedly, and then like clockwork every day the sell side returns just as strong as the day before. This happens a little in most stocks, but none so dramatically and consistently as it happens on LYC, whilst the buy side remains similar strength both day and night.

I assume its coz they are props or dummy bids etc, but I can't figure out what benefit they gain from disappearing at night, only to reappear just as strong once trading starts the next day. Why not just leave them there overnight to make them seem more real?