Stever22

I tried the disable all plugins and change theme to standard theme and still did not work. I installed the WP Downgrade plugin and downgraded back to 5.0.3 and installed a Disable Automatic Updates plugin to prevent it automatically updating back to 5.1.

Weird thing is some say could be PHP version. The site having he issue has a newer version of PHP than the other site not having an issue.

I am getting the same thing. The only way for me to edit or create Posts or Pages is to disable visual editor under Users-Your Profile. On another site I maintain and upgraded to WordPress 5.1 everything works fine.

Interesting. I just checked another website I maintain. It has the latest Wordfence installed. It also only has 64Meg on the server and it seems to be working fine (except when I run a scan). My other with 64Meg would not even open unless I logged in. Now this site has very limited add-ons. Its using 33meg of the 64 meg. Again I still believe it has to do what is free. I ran the Test your wordpress host’s available memory and it fails with a similar error message but at least the website runs OK.
My conclusion is Wordfence is a pig on memory. You can set the maximum memory that wordfence can use to whatever and it does not really do anything. You need free memory.
Wordfence. What does the maximum memory that wordfence can use really do?

I had my webhost increase the memory to 128 Meg and now the error has gone away. I tried all the other suggestions above before memory increase and it never helped. I believe its related to the amount of memory that you have free. I use an add-on called Server IP and Memory Usage (https://apasionados.es/#utm_source=wpadmin&utm_medium=plugin&utm_campaign=server-ip-memory-usage-plugin) and before with 64meg I had less then 10% free. Now I have 60%. Also I set the max memory that Wordfence to use to 20Meg but during a scan it says it used over 32Meg of memory to scan.This limit really does nothing for me. Oddly Active says he has 255Meg and still gets the error. How much memory do you have free?

Thanks,

Steve