Skipping chunk X of Y.Z because MySQL chose no index instead of the word_sid_typeindex

Skipping chunk X of Y.Z because MySQL chose no index instead of the word_sid_typeindex

My environment:

# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 6.8 (Santiago)
# uname -a
Linux A.B.C 2.6.32-642.4.2.el6.x86_64 #1 SMP Mon Aug 15 02:06:41 EDT 2016 x86_64 x86_64 ...