I don't know if its just me, but I observed that my speed becomes lower compare to previous days. I got only around 480 mh/s average while last month is around 500-504 mh/s. This happens to 4 of my L3 and running on a different locations
Check your power supply units. Are you getting enough power per miner?
Are you over/underclocked? This happens to some miners when they accidentally/unintentionally overclock/overclock.
How much downtime did you experience? Check your logs. Sometimes, a miner might just refuse to hash for a while.
For me, my L3s are happy and running just a little underclock since my power supply units are pretty... questionable.