Prohibitory Sign, Then Boots

Hey Guys. Still working on the same MacBook Pro.

The MacBook Pro gives me a Prohibitory Sign on startup, but then boots fine.

No real problems, I would still like to know why I am getting a prohibitory sign for only five seconds, and then the Mac boots fine. I am using High Sierra, so I am not using an patchers.

crwdns2934089:0crwdne2934089:0 crwdns2934093:0crwdne2934093:0

crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 0
crwdns2934285:0crwdne2934285:0