Connection issue with NPM and guacamole from some computers

Ive setup guacamole as a proxy on NPM with ssl. It works on most private remote connections (i.e. my friends or parents house, or through cellular network), however I cant access when I use a remote computer connected to a corporate pc that is behind its own proxy.

When trying to access my guacamole server on my own domain, instead of login screen I get this error page:
"An error has occurred and this action cannot be completed. If the problem persists, please notify your system administrator or check your system logs."
It is worth to mention that rarely, once a day, I manage to get to the login screen after hours of randomly refreshing the page.

I can`t figure if the problem is in NPM or guacamole, but I suspect the problem to be a proxy/routing issue. Ive tried turning on/off all ssl settings http/2, HSTS, as well as common exploits and websockets.
Anyone know what might be the problem?

Start by reproducing access through the corporate proxy and inspect the Nginx Proxy Manager and Guacamole system logs. Compare the proxy, SSL, HTTP/2, HSTS, and WebSocket settings with a connection that reaches the login screen. Done means identifying whether Nginx Proxy Manager or Guacamole causes the failure and documenting the relevant configuration or fix.