To anyone getting memory limit errors no matter how much memory they give wordpress –
The issue is not your memory limit, the issue is iThemes security.
Disable backups altogether in iThemes Security. It tries to load your entire database into memory, and it does this multiple times a day (even if your backup is scheduled for every few days or once a week or whatever). It makes no sense, but this is happening, and it is the most likely culprit since the wp-db is throwing the memory error. Use something else for backups, maybe even backup your full account through cpanel if using shared hosting instead of just backing up wordpress. I’m not advocating the idea of ditching backups, I’m advocating not using the backup feature of iThemes Security.
These options are easily accessible through the iThemesSecurity dashboard, you just have to turn them off completely.
I just spent a year on and off having page loads fail, and I did everything from moving to bigger better servers to spending hours spinning my wheels. This was the fix.
Other than this, this plugin is fantastic.
