Interesting discussion here on reddit:

https://www.reddit.com/r/meraki/comments/41laj8/did_the_z1s_just_get_a_bandwidth_lock_pushed_down/

 

Apparently they were only ever rated for 50Mbps, but now they're enforcing that as an upper limit rather than allowing it to have higher throughput.  Which sucks for anyone who already was using one in a situation that was working with a higher throughput.