Seahub 7.0.5: ValueError: unsupported pickle protocol: 4

Trying to install seafile 7.0.5 on Ubuntu 18.04.
Seahub started successfully, but when I try to access http web interface, I see the error:

Page unavailable
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And in logs there are problem:

2020-01-21 09:44:15,101 [ERROR] django.request:135 handle_uncaught_exception Internal Server Error: /admin
Traceback (most recent call last):
  File "/opt/seafile-server/seafile-server-7.0.5/seahub/thirdpart/django/core/handlers/", line 41, in inner
    response = get_response(request)
  File "/opt/seafile-server/seafile-server-7.0.5/seahub/thirdpart/django/core/handlers/", line 244, in _legacy_get_response
    response = middleware_method(request)
  File "/opt/seafile-server/seafile-server-7.0.5/seahub/seahub/base/", line 68, in process_request
    cur_note = cache.get('CUR_TOPINFO') if cache.get('CUR_TOPINFO') else \
  File "/opt/seafile-server/seafile-server-7.0.5/seahub/thirdpart/django/core/cache/backends/", line 40, in get
    if not self._is_expired(f):
  File "/opt/seafile-server/seafile-server-7.0.5/seahub/thirdpart/django/core/cache/backends/", line 137, in _is_expired
    exp = pickle.load(f)
ValueError: unsupported pickle protocol: 4

how can I fix it? Maybe downgrading can help?

Looks like python2 and 3 are somehow mixed. Python 2 and from 7.1 on python3 has to be used (which is good because python2 is eol)

Yes, thanks, there are some mixes after I try to install 7.1 version and got issue Seafile server 7.1.0 is ready for testing! Migrate to Python 3

After cleaning up all old files and settings, this error is disappear!