Hi @fra8719,
I’m not able to replicate any such issue when tested with Hustle by creating a new Popup and by adding new opt-in fields. I could delete the newly added fields instantly once added.
It sounds more like an existing plugin causing a conflict. Could you please run a conflict test and then see whether the issue still exists?
Please check the following flowchart on how to run a conflict test:
https://premium.wpmudev.org/wp-content/uploads/2015/09/Support-Process-Support-Process.gif
Please do let us know how that goes so that we could check further if needed.
Looking forward to your response. Have a nice day ahead.
Kind Regards,
Nithin