Cannot run ghost update

Hi all, thanks in advance for all your help. Ghost worked perfectly fine so far, until I tried updating it from command line once again. Below follows information on the error in detail:

Version: latest on NPM
Configuration: Ubuntu 18.04 LTS, Nginx, Digitalocean

Errors:

$ ghost update
/usr/local/lib/node_modules/ghost-cli/node_modules/any-observable/register.js:29
		throw new Error('Cannot find any-observable implementation nor' +
		^

Error: Cannot find any-observable implementation nor global.Observable. You must install polyfill or call require("any-observable/register") with your preferred implementation, e.g. require("any-observable/register")('rxjs') on application load prior to any require("any-observable").
    at loadImplementation (/usr/local/lib/node_modules/ghost-cli/node_modules/any-observable/register.js:29:9)
    at /usr/local/lib/node_modules/ghost-cli/node_modules/any-observable/loader.js:30:18
    at Object.<anonymous> (/usr/local/lib/node_modules/ghost-cli/node_modules/any-observable/index.js:2:39)
    at Module._compile (module.js:652:30)
    at Object.Module._extensions..js (module.js:663:10)
    at Module.load (module.js:565:32)
    at tryModuleLoad (module.js:505:12)
    at Function.Module._load (module.js:497:3)
    at Module.require (module.js:596:17)
    at require (internal/module.js:11:18)

To reproduce: try sudo npm i -g ghost-cli@latest and ghost update

What could be the reason for this? Thank you.

The issue also happens on ghost help and any ghost-cli command.

After manually installing rxjs via npm, the error becomes this:

$ ghost update
_http_client.js:106
    throw new TypeError(
    ^

TypeError: Agent option must be an Agent-like object, undefined, or false.
    at new ClientRequest (_http_client.js:106:11)
    at Object.request (http.js:38:10)
    at Object.request (https.js:239:15)
    at get (/usr/lib/nodejs/got/index.js:49:18)
    at Immediate.setImmediate [as _onImmediate] (/usr/lib/nodejs/got/index.js:124:3)
    at runCallback (timers.js:810:20)
    at tryOnImmediate (timers.js:768:5)
    at processImmediate [as _immediateCallback] (timers.js:745:5)