ModuleNotFoundError: No module named 'seaserv'

Upgrading from Pro v8.0.14 to v8.0.16 following maintenance release process of running ./ Seafile starts fine but on starting Seahub, I get this error:

[root@hobbiton seafile-server-latest]# ./ start    

LC_ALL is not set in ENV, set to en_US.UTF-8
Starting seahub at port 8000 ...
Traceback (most recent call last):
  File "/data/seafile/seafile-pro-server-8.0.16/", line 19, in <module>
    from seaserv import ccnet_api
ModuleNotFoundError: No module named 'seaserv'

I’ve rolled back to v8.0.14 as this is a production system.

Supplemental information: upgrade from v8.0.14 to v8.0.15 works fine (Seahub starts fine) but same error occurs with upgrade to v8.0.16, i.e. the error occurs in v8.0.16 alone.