Dashboard gone, widgets missing, unable to show graphs

[Baatun]

Hello, Zabbix community!

I am currently experiencing a weird problem with my Zabbix. After installing SMTP on Zabbix server and enabling Email notifications (I am not sure if it is connected with this) my dashboard widgets disappeared. I can not create a new dashboard, add widget or edit. The frontend is not responding. Second weird thing I am experiencing is that my graphs are not showing. Zabbix is a new thing for me.
Please help, thank you in advance.

Edit: found another problem. When editing item, changing item type doesn't change input fields. (see screen)

[Baatun]

SOLVED: the problem was with the firewall on another device.