A restore also reconfigures all webserver configuration files. This process can take several minutes, depending on the number of configuration files that need to be created. The process first deletes all such files and then restores the files for each subscription separately. It is correct that during this phase the web server points all traffic to the default page, because the web server does not know the virtual hosts yet. This is an unavoidable behavior. I can think of ways how this could be done better, e.g. create all new config files in a shadow directory and then move them into their destination all at once, but currently it's a one by one algorithm.
It is normally not necessary to run a "plesk repair web" on it. This will only reconfigure the server again. Instead, when the issue occurs, look into the system with
# ps aux | grep mng
or
# ps aux | config
which will reveal the ongoing reconfiguration processes.