So, I found an old cable that was being used to uplink the Z from the ISP - replaced it and its now running at 1G
I also replaced the unmanaged switch with a managed (non-Meraki solution)
So far so good. If I continue to run into errors my next steps are to factory reset the Z1, or connect my switch directly to ISP and bypass the Z to confirm.
I've got a feeling (fingers crossed) that the managed switch will do the trick. I noticed that before the Z1 drops, the APs are down for quite a while. The APs went down as soon as staff started to arrive this morning (first clients on network since friday), then the Z1. I think the unmanaged switch was creating a loop between the two APs.
Time will tell - I will update