Is this a ban?

Nope, you just don't have an internet connections or the servers were down.

Restart your steam and it might should be work.

DbD serivces or steam, idk now laggy. I has many times went out of lobby.

If you get banned you will get a message that you were banned.

There's 3 things I know of and I feel it'll be the third. But either it's your internet acting up, servers are down or if you're steam sharing, the steam share is off / not working correctly so just go back on to the main account you shared it from and just re-enable it.

its not check your net like others said

yes its ban , just check in steam profile , game ban record = banned