Usually it's service references that cause delays when they have to wait for services to be published, so this is very odd. Please check that little CPU is being consumed during the delay as high CPU consumption may be a clue.
You may find it helpful to look in the serviceability/logs/log.log file. You can configure what goes into this file by modifying config/serviceability.xml - the simplest change is to increase the root logging level from WARN to INFO to get more information.
As you can see, this is along the lines of "teaching a man to fish"...