Hubconnect has worked flawlessly for me for quite a while. I have the server and a client on one lan and a client on another remote lan. The server and client work local but I cannot get the reomte client online. The error on the client side reads 
Instance in use by another hub.
Thanks
I had a random hubconnect issue with the same thing after updating my c7's to the latest firmware. The remote hub went offline and I couldn't get it back on. However, randomly, after a few hours it came back online... That was only after the latest firmware upgrade... fast forward a few days...
got my new c8's and did the switch. same observation as you, the local lan hubs were fine, but the remote hub was once again offline.
I figured it probably had something to do with the connection key possibly changing with new hardware? So I ran the connection routine again, copying the connection key over to my remote hub and all is working again... I truly have no idea if the key changed with the new hub, but thats what I did and I'm back up...
It could also have something to do with the new firmware, as I had the same problem with the c7's a few days earlier. again, only between hubs at different locations. both times, both hubs on the same lan were fine.
I have tried the key several times. I did the upgrades 36 hours ago. Still working on it. I keep talking myself out of deleting it and starting over. ( just the remote hub) But they are seeing each other because the error thinks the remote hub is already connected.
There's a set of places to look/try:
That's in Server, for each Remote.
Still on Server, there's a device for each Remote. You can click Off and then click Initialize.
There's the same device on each Remote hub (usually named Server Hub) and you can do the Off then Initialize.
I removed the instance before your response. Reset it up Both sides online and connected. Now resync is missing on the server side for devices to be brought over.
Download the Hubitat app
