if I knew what are the lines that really produce the memory errors that could be doable.
At lot of the time it is just like:
[11-Apr-2018 18:41:45 UTC] PHP Fatal error: Allowed memory size of 201326592 bytes exhausted (tried to allocate 20480 bytes) in /wp-includes/plugin.php on line 449
In these cases the failure to allocate 20480 bytes is a symptom of something having eaten all the memory, not the cause.
It all stops though when WJECF_AutoCoupon is disabled.