Upgrading from 2.3.3 to 2.5.0 induces error "Handler not found"

[niklasjoh]

As stated in title, we upgraded from 2.3.3 to 2.5.0 package of resclient.
Now we notice a lot of errors where we try to .off() on listeners, there are "no handlers".

    unsubscribe() {
      if (this.sub?.off != null) {
        this.sub.off();
      }
    }

Where unsubscribe is called from beforeUnmount-hook in a vue component.
Generating errors in console