There's some magical limit on number of segments that a single user can create. Hell only know why there's such limit and why total number of segments is limited per... 16 hours not per full day or 24 hours.
But the best part is a notification to let you know that you've passed the threshold:
You see it after you created a segment (and failed to do so)!
In other words, you can click-out your segment as a complete moron only to hit the wall that you failed to create it due to limits enforced on you by Strava.
Strava engineers are too stupid (or too ignorant) to warn you that creating new segment is pointless before you start creating it.
Of course it completely doesn't matter whether you are paying to Strava or not. This stupid limitation is enforced equally for both free users and paid subscribers.