After building the grin (following this guide: https://github.com/mimblewimble/grin/blob/master/doc/build.md) into my bash Ubuntu 18.04. I’ve never been able to get my instance to sync. The ‘connected peers’ : number also does not exceed 2, and I am stuck on chain height 0.
Looks more like your setup. I saw no problem on > 10 different Ubuntu testnet 4 setups.
The only time I didnt found peers on one host, I fixed it by switching seed type: from “DNSSeed” to list of hardcoded healthy peers (in the grin-server-config file).