I think I have found the issue. After rebooting this time everything was still there.
I suspect the "extend trial license" of Unraid (I wanted to wait before buying, since I'm getting a new connection on Tuesday and with my ISP I'm not sure if they will actually provide an IPv4 address) is responsible. This time I didn't have to extend the license and everything was still there.
I've attached the diagnostic anyway, just in case.
Array not started skynet-diagnostics-20200529-1932.zip