pgAdmin4.15: 500 Internal Server Error

Pgadmin4 isn't working after upgrading to 4.15
(Was working before the update in server mode on wcgi)

I set the following in config.py:
  DEBUG = True
  CONSOLE_LOG_LEVEL = logging.DEBUG
  FILE_LOG_LEVEL = logging.DEBUG
I restarted apache2
Visiting 127.0.0.1/pgadmin4 gave the attached pgadmin4.log

My system:
    Ubuntu 19.04 with the postgresql apps from apt.postgresql.org

Installed packages:
pgadmin4-(apache2,common,dbgsym,doc) 4.15-1.pgdg19.04+1

Any help appreciated,

Regards,

Bastiaan