Customizer not working properly with W3 active

Hello,

We have a multisite where W3 Total Cache is active. We were having issues when we’re trying to save changes using customizer, with the following error:

“Looks like something’s gone wrong. Wait a couple seconds, and then try again”

Even having that error, the customizer works fine (it saves the changes, but displays the message). We’ve deactivated all plugins and narrow it to W3 Total Cache. If we have it active, we get that error. If not, everything works fine and we get no error at all. Trying to disable W3 Total Cache features doesn’t work either, but we can’t disable the Opcode cache (even though we don’t think that could be the issue).

Other things we’ve looked into is that we have an error when we use the Health Check plugin (though it could not be related at all with this issue):

“The loopback request to your site failed, this may prevent WP_Cron from working, along with theme and plugin editors.”

Why are we getting that error message even with the plugin working fine? Is it possible that W3 Total Cache has some issues that are making us have that error? What can we try to solve it that we could have missed?

Thanks in advance. Kind Regards,