Help please, I'm really stuck!
I have a custom module (ObserverInterface) to construct all my menu. When de Cache is on, you can see this module only in few pages.
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jajajaja, it was easy!!! Instead of the menu, we had a "esi:include" tag. This tag supposed to be rendered by the Varnish Cache.
The thing is that we don't have the Varnish cache instaled, but the configuration for Caching Application in Store > Settings > Configuration > Advanced > System, in the Full Page Cache section, was "Varnish Caching".
Easy to fix, change Varnish Caching for Built-in Application (of course if you don't have the varnish installed).
Thanks to every one!!