There is a bug in the Community Events list function. When you list out community events you have entered, the venues are shown as active links. When you click on a venue link, it opens an editing form. Unfortunately, the form does not contain current state of the venue item, but instead always shows an empty form, even for existing venues. If you save the form without re-entering all the venue information, the venue data will be lost.
This is a bug. The link to venues should bring up an editing form populated with the last saved state of the venue item, allowing the user to edit it if desired.