I can confirm the registration problem:
waptserver.log:
2019-03-25 14:02:14,450 WARNING Websocket connect params: Unable to get auth token: Error on server:
EWaptAuthenticationFailure(u'Unknown host UUID 01962215-7F3A-7A4C-BF90-F76BF79F6844. Please register first.',)

I'm not far from...

Here is the wapt-get.ini file on the agent that is not registering with the WAPT server:

[global]
repo_url=https://MY-WAPT-SERVER.DOMAIN.LAN/wapt
send_usage_report=1
use_hostpackages=1
wapt_server=https://MY-WAPT-SERVER.DOMAIN.LAN/
use_kerberos=0
check_certificates_validity=1
verify_cert=C ...

Note:
I do not use Kerberos authentication, so I modified the line in the /opt/wapt/conf/waptserver.ini file
allow_unauthenticated_registration = True
, replacing allow_unauthenticated_registration = False (default).

Hello,
I have a very similar problem: (some of the information presented here should help some people configure their GPO ;) )
the GPO is deployed, the WAPT service starts, but the computer doesn't register with the WAPT server.

I have to do it manually via a "wapt-get register" command online...