In the UI: Config Template | Security & SD-WAN | Routing | Subnets | Add VLAN | Subnet UI
Setting the subnet mask for a 10.0.0.0 VLAN has a bad UI issue. The user will set the subnet mask THEN the IP address (because data entry is left to right). However, setting the IP address to a 10.x.x.x address UNSETs the value in the subnet mask back to /10.
The user must then RE-ENTER the subnet mask.
This is counter-intuitive and not easy to spot.
Fix needed.
Author, https://www.nuget.org/packages/Meraki.Api/