[Plugin W3 Total Cache] displaying blank pages with memcached

Have recently enabled memcached 1.4.4 for W3 total cache 8.5.1 and experiencing a rather frustrating problem.

For some users (logged out visitors) visiting the site they’re presented simply with a blank page, no content, no source, this affects all browsers and is intermittent.

This only appears when memcached is enabled for page cacheing and fine for all other cacheing. If i turn it off the site displays fine, turn it on, goes again.

Have very verbose logging on memcached, can’t confirm it but i’m seeing a few

28: going from conn_parse_cmd to conn_mwrite
28: going from conn_mwrite to conn_new_cmd
28: going from conn_new_cmd to conn_waiting
28: going from conn_waiting to conn_read
28: going from conn_read to conn_parse_cmd
<28 set w3tc_f7016b02e84e438f9dbd2d3ce481368f_sql_056e6bad1a5ab5a443ae8728f63e0bcd 1 180 516
28: going from conn_parse_cmd to conn_nread
> NOT FOUND w3tc_f7016b02e84e438f9dbd2d3ce481368f_sql_056e6bad1a5ab5a443ae8728f63e0bcd
>28 STORED

and there are no errors in the apache logs

stumped

any suggestions ?

Regards

R