The error happens in Unyson 2.7.6 version.
Please follow the instruction below to fix it
- Deactivate all your current cache plugin
- Deactivate & Delete Unyson plugin
- Download Unyson plugin here
- Go to Plugins -> Installation -> Upload plugin, then upload & activate Unyson plugin
- Download the plugin here and install to your site. If you get the error message after activating this plugin, it's normal.
Back to your page, you can see the content now, if you don't please try to delete your browser cache.