The warning is not relevant to the problem you are seeing unless you used --classic to try to turn off the confinement? In that case I think --devmode is the flag to use.
note that --devmode disables automatic updates for the app (while it turns off bits of confinement, it is really what it says, a developer mode (it will also produce a lot of log output))…
yup, interface connections are a one-time thing after fresh install of a snap. they persist for the lifetime the package is installed (unless you call snap disconnect ... on them).