Ahoj Ivan,
Thanks for reaching out! I’m sorry you are having a problem, let me try to help you.
If it was working fine before the update, then there might be an issue with WP 4.6 or WP 4.6 and our plugins working together. I will need to investigate that.
I have tried to recreate the issue you posted: I tried to submit a new community event with Visual Editor and with HTML editor. For me both of them worked fine.
Could you please share your system information with me in a private reply? That might shed some light on this issue.
Here’s a handy guide how you can do that:
https://theeventscalendar.com/knowledgebase/sharing-sys-info/
Also, did you try this with switching to a default theme like twentysixteen? Please give that a try and let me know the result.
I’m afraid I am not able to help you with WP-Smush as that plugin is not developed by us, unless it is somehow conflicting with one of our plugins.
Diky,
Andras