Interesting… I have at least 10 team members who have this issue.
From Travis in August 2020: It’s kind of a known “issue”. We just don’t know exactly what causes iOS to disconnected the “VPN”.
We’re looking in to an “always on” feature, but I don’t have a ship date on that yet.
Then in February 2021: Unfortunately we don’t have a timeframe for this. Will definitely add your comments to the open issue we have and try to get it bumped up in priority.
There’s also this thread from September: ZT on IOS will silently disconnect after some time
And this one from October: Always-On for iOS