I think the reason for the "drop and restore" hashrates we see up there is a combination of: ASICs being kicked out and switching to other, not-yet ASIC resistant coins, miners that don't change their infrastructure and submit invalid shares for a period of time, miners that use e.g. nicehash etc. and don't update their miners on time, so that they will stop getting proper work until they're updated to support new algorithms, web mining scripts that are not updated in time and last but not least, botnets that are not able to "update" the mining code on their victims instantly.
All these reasons added together might cause the impact you see on the chart.
But in the end, it's just speculative