As far as I've experienced, you need quite a few warning messages to get an online ban.
I'm SDing or disconnecting every time the match is too laggy to be enjoyable (don't blame me, blame those people playing on WiFi =') ) so I've got a few of them since release, but never got a ban.
Fun thing, I got a warning after being disconnected due to server maintenance
That being said, I've notice more communication error yesterday compared to before. I don't know if it's due to a change they made or not but I had like 4 or 5 times this message. Always happened when trying to start a match though so no penalties but it's definitely weird. I know it's not coming from my end, I am still using a LAN adapter and my connection doesn't suffer from any instability or disconnection.