NCBI will be testing https on public web servers from 21:00 
p.m. Monday, Sep. 26st, until 1:00 a.m. Tuesday, Sep. 27st.

You may experience problems with NCBI web sites during that time.

details:
https://www.ncbi.nlm.nih.gov/home/bulletins/https-tests.shtml
(RelatedURL1)