Replications including test replications never get triggered. The browser hangs indefinitely.
Thread dumps show a thread stack:
AEM 6.2 or later
Assuming the stack trace is the same, then the root cause is likely due to a custom ACL package being installed. The custom package would have deleted the out-of-the-box ACLs on the root repository node.
If you are on AEM6.2, then install the attached package OOTB-acls-1.0.zip to apply the ACLs. Then install your custom ACLs again, but first rebuild the package using the AC Handling mode Merge.
If you are on a later version of AEM, then create a package from a fresh install. The package should have the following rules: