That looks like it is probably from an improper field value. I can see what would potentially cause an notice like that, but can’t force it to be reproduced in testing (i.e. I’m not getting the same when excluding an expected value)

The section in question would be for the value settings of a select, multiple select, or membership field (“membership” fields are a “select” field type but you don’t input your own values).

Regardless of whether it’s the result of invalid values in the field, or something in the plugin, I’d like to determine what it is so I can either return a valid error message or correct whatever is invalid. But I’ll need to be able to reproduce it.

Go to the plugin’s support site and open a request through the support form. Reference this thread, and I’ll respond with instructions on how to send me a copy of your settings.