Hi,
with reference to the following topic:
https://wordpress.org/support/topic/404-page-not-found-error-and-internal-server-error?replies=2#post-7790695
This unfortunately does not work.
Last night I tried also to downgrade WP to 4.3.1, and there is still the same problem. I looks that upgrade to 4.4 Clifford was not the main problem here.
I have approx. 7000 files uploaded already.
Could I ask You for more help and to check my installation?
Greetings
Thomas