Hi bahsig,
my problem was that I tried to start a 3rd party script (ElasticSearch Beats binary in my case) via the shellcmd package.
As Beats is not a service by default it ran as a program and didn't provide an exit code to shellcmd.
So in the end shellcmd waited to infinity for Beats exit code.
Due to the daisy chaining of shellcmd in the PfSense / FreeBSD boot process it blocked the machine from booting. ;-)
Once I killed the binary from the console / SSH booting finished and PfSense worked as expected with syncing, etc.
Sadly there is no alert or system stat that shows you the FWs "boot state". ;-(
Hope that helps.
Michl