Restart of the program seemed to fix it.. I'm sure all other fields were clear.. that's odd.
This issue sometimes happens if an index for your file gets a bit messed up. You might try importing all your records into a clone of the file. Importing the data into a clone will rebuild indexes "from scratch" and that sometimes fixes the problem.
Is for the @ symbol, just find the email addresses with quotes.
is something about wildcards or something like that.... you can find more info here: