@cherry856
I am just a humble user of Wordfence. I've experienced the following, which holds for WP sites that are not too big or complex:
. a hosting setup with 64 Mb is tight and sometimes too small.
. usually a setting of 50 or 55 Mb is needed to get things working.
But again: it all depends on how big your site is, how much and what plugins you are using.
If you have a minimum of 128 Mb available and you have the setting at 80 Mb I guess things will go alright, usually.
How much memory does your hosting account have? And what is your setting in Wordfence? Does that work for you?
Mark might be able to elaborate, but this is what I have found so far...