in your nginx odoo file (example: /etc/nginx/sites-available/odoo ) add this in the begining of the file:

map $http_upgrade $connection_upgrade {

    default upgrade;

    '' close;

}

Then add this lines in "server" section: 

    # Soporte para WebSocket

     proxy_set_header Upgrade $http_upgrade;

     proxy_set_header Connection $connection_upgrade;

This worked for me

Try updating to the latest version. We encountered a similar issue, and after updating the module, the problem was resolved. Keep in mind that if you have any third-party apps installed that directly affect your spreadsheets/documents module, you will need to update those as well."

Same thing for me

Hello, I am also facing the same problem, is there any solution to fix this problem?

any solution yet?

Same here, does anyone find something useful

Same thing for me :( 

Hello Admaja, faced the same thing, have you resolved this problem ?