Upload error thrown after update to latest version

Hi there,
I’ve updated to the latest version and I’m experiencing some issues.
On my anon upload form I have a notice at the bottom of the page and it says ‘Image will be deleted when saving your changes if unused by others.’ – what’s this for and how could I get rid of it?

Also, I’m getting error thrown every time I upload a dummy event, I have it set to any file type and no limits added in the settings anywhere. I’ve increased the max file limit high enough that there’s no way that’s an issue either. But I get this em error each time I upoad:
“Uploaded file type not allowed. Permitted file types are:”
Although it doesn’t list any file types.

Any tips appreciated I’m completely stuck, to test, I tried setting the config to

define(‘ALLOW_UNFILTERED_UPLOADS’, true);

….it didn’t help though.

Grateful for any assistance, my front end upload is out of use until I fix this.
Using latest version of wp etc, and have tested plugins by turning off, no success yet 🙁