Sync is not working when the data not change in the long time

Hi all.
I’m developing a mobile app for iOS.
I open app, keep it running, not change data from server replicated in 30minute.
After I try to change the data on server replicated. But the new data not sync to the app.
Current network status at this time is “Closewait” not “Established”:

Until i call function [CBLReplication restart] of pull replication.

But I am worry about call “restart” function. because i see the another connection after each call it. See below:

What configuration on CBLReplication to make sure it always synchronous?
This is my configuration:
pull = [_database createPullReplication:syncURL];
pull.continuous = YES;

Thank you for any idea.