It seems like I read that the Tesla server was going to be down in the middle of the night a couple of nights ago. I had the same problem, deleted and reinstalled the app, and it is doing fine for me now.
I saw "Unknown Error" the other day, but have been getting "Network Timeout" more regularly. I thought this was something tied to 2018.20 (I had a similar issue on Sunday, which eventually got fixed by car reboot despite it seeming like an app/cloud problem). The last day or so I've been getting only intermittent connections though: https://teslamotorsclub.com/tmc/threads/app-connectivity-issues-again.116395/