OP is referring to ZeroTier 2.x which makes it easier to run your own control servers (called root servers in ZT). Any connection flakiness is probably due to

OP is referring to ZeroTier 2.x which makes it easier to run your own control servers (called root servers in ZT). Any connection flakiness is probably due to NAT or firewall issues and is going to occur in any P2P network layer since they all use a toolbox of common techniques such as UDP hole punching.