Hi Dan,
from the above info difficult to guess. what you can do it first capture sip trace in SIP server side and see if register message is coming. if not it is to be debugged in baresip side.
one option is check if the IP address can ping to server IP.
SIP side also some times slow and does not reply if invalid message discard.
you can capture PCAP or other message of SIP and attach for others to help.