On reboot of a VyOS router, I observed it sending the peer a CEASE (peer de-configured) followed ~60ms or so later by a CEASE (administrative shutdown). My understanding (which may be incorrect) is that only one CEASE should be sent.
As seen by a BGP peer (non-VyOS) at time of VyOS router reboot:
2020-02-01T00:12:35.441721Z [N] «8» 0 BGP NOTIFY CEASE Peer-Deconfigured 2020-02-01T00:12:35.506884Z [N] «9» 0 BGP NOTIFY CEASE Administrative-Shutdown 2020-02-01T00:12:35.566658Z [N] «10» 0 Closed connection