More often than not they usually take down the hashrate few days before diff jump to male it appear smaller
Our equipment runs 24/7 (sha and scrypt), our uptime is >99%. Taking our miners down for several days would not make sense from an economical perspective.
My best guess is that some big ASIC company shuts down a massive mining farm (we are talking of 20 PH/s) of outdated hardware, in order to prepare it for new hardware.
Best regards,
Marco