Using 7.0.3 CE Version (compiled to raspberry pi)
FILE_SERVER_ROOT = 'https://xxxxx.xxxx.xx/seafhttp'
SERVE_STATIC = False
MEDIA_URL = '/seafmedia/'
COMPRESS_URL = MEDIA_URL
STATIC_URL = MEDIA_URL + 'assets/'
SITE_ROOT = '/seafile/'
# Since version 5.0.4 we need to define this as well:
LOGIN_URL = '/seafile/accounts/login/'
The config was not changed. Seahub cache (in my case memcached) was empty. I tried deactivating memcached as well, and flushing seahub_cache.
root@hiperborea /home/seafile/logs # tail -f seahub.log
2019-07-16 19:13:24,725 [WARNING] django.request:152 get_response Not Found: /seafile/seafmedia/avatars/f/1/2278a8042266053fc3e798fb5e2f40/resized/72/1fb9e7bb2be3e0fa49a3655ef7fdbac3_o8NwnS5.png
2019-07-16 19:13:24,727 [WARNING] django.request:152 get_response Not Found: /seafile/seafmedia/avatars/f/1/2278a8042266053fc3e798fb5e2f40/resized/64/1fb9e7bb2be3e0fa49a3655ef7fdbac3_o8NwnS5.png