Hi Ingrid,
I’m sorry to hear you’ve hit up against some difficulties.
My hunch is that this is indeed a conflict of some kind and if you didn’t deactivate all other plugins (except for The Events Calendar) then doing so is probably worthwhile.
I realize that may not be a step you are comfortable with on a live site, so a good alternative is to create a test site (which can be as simple as a fresh installation of WordPress in a subdirectory – ie example.com/test-wp – which is something most hosts make pretty straightforward) and add only The Events Calendar and your Event Aggregator key to begin with.
Confirm the problem doesn’t happen there, then begin adding the same plugins and ultimately the same theme as you have on your live site. Hopefully, you can then discover which component is triggering the conflict.
Would it be possible to give this a go?
Thanks!