This is because value of 'innodb_log_waits' most of the time remains to '0' and We do not always INSERT into [snapshot_master]. Only if the particular metric was changed since last time something was INSERTED for that metric we will INSERT again. So if you want to find the value of a metric at some particular time you will need to find the most recent value stored before that particular time for that particular metric.
MySQL documentation says `Innodb_log_waits` – The number of times that the log buffer was too small and a wait was required for it to be flushed before continuing.