Is it normal for this hash to go down to zero and back up again then every so often or should it remain consistent?
it depends in which pool you are mining, also the temperature it has the ASIC
if you mine in nicehash, you will get constant "equal" hash because you are selling it.
if you mine in other pools, then the hash will throttle less or high depending in which pool.
it throttle when it's mining another coin (when changing to another coin) also it depends of the difficulty at the moment.
the ASIC has a temperature protection, so if reach at a certain number, then will reboot.