When Strava is having trouble, NavRun tells you on the site too, then brings in the runs it missed.
Strava's own API goes down sometimes, and a run you saved during one of those stretches used to sit invisible until a full sync caught it up. Now, while Strava is having trouble, a note on the site says so, once per outage, so a run you just saved is never mistaken for lost. Once Strava is back, any runs from that window come in on their own, with no action from you.