Hash_on_header on kong version 2.6

[sachinrana50]

while enabling hash_on header on Kong, i am not seeing 100% success of hashing, although it is above 90%, not sure why, even i am not sure why hashing is not working 100% even though configuration is very simple just enable hash_on header and header value.
also, i have enabled debug log_level still nothing is printing over logs why hashing and upstream not working.

please support.