New Static Lease Not Saving 19.07.0-rc1

I wanted to add the static leases back because the upgrade cleared my config. I added the static leases back and for the first couple of mac-addresses and IP-addresses it worked (the devices already had the "old" IP-address, which was nice). But for this one it did not work. I refreshed, rebooted, tried different ways but the save box keeps on turning (at least 15 minutes have passed) and nothing being applied or saved.
I added 5 static leases already, updated LuCI (via opkg upgrade (all list-upgradable)) to git-19.324.
This is not a problem for me now, but something I am not sure of if I did something wrong or if this might be a bug.