There seems to be a bug in the calendar view when there are multiple activities. I can’t delete the activity there (I did manage to do it in the list view).
I made a screen recording of it here:
This is in the latest Google Chrome on mac.
Your screen recording link isn’t working for me but you can create a support ticket by emailing support@xertonline.com.
I don’t know why it embedded a link that does not play. I’ll mail the link to the file.