Problem after upgrade 3.5.5 to 3.6.3

[rvdk92]

Hello,

I do a update like always:

cd /opt/netbox
sudo git checkout master
sudo git pull origin master
sudo ./upgrade.sh
sudo systemctl restart netbox netbox-rq

I cam from 3.5.5 and updated to 3.6.3, but i can't open netbox now.

The service is started fine, but when i browse to Netbox i get a Internal Server Error. only fault that i see in syslog is:
Oct 4 13:30:18 netbox python3[2346]: from drf_yasg.utils import swagger_serializer_method
Oct 4 13:30:18 netbox python3[2346]: ModuleNotFoundError: No module named 'drf_yasg'

Can anybody help me how to fix this?