Can not save unit in create items

Hi I’m now evaluating erpnext system.Install it is not easy but finally made it through docker install. But now has a problem when i try to crate a new item in stock. The unit can’t save .

The new unit can be crated and found through the search, but once i click it try to use it for the item is disappear.

any one can tell what’s the reason ? i’m new to linux and also erpnext