1- Access any computer via Agent Browser and click proxy. Select HTTPS from dropdown, enter the IP info on the right side, click start.
2-Login to Synology NAS, go to ControlPanel\Users&Groups, select the user unable to connect to the share, double-click.
3-Click “Sign out of all devices” and try accessing the share again. If that does not help, reset the password to the same password and sign out the user one more time.