Form submission sometimes gets a 403 page

I’m getting emails from users of my site who are getting a “403 Forbidden Error” after submitting a form (e.g., product rating/review in woocommerce, gravity form, even after checkout).

It doesn’t seem to happen all the time – just now and then. But enough that’s it’s generating email inquiries.

Anyone else ever see this?

Joe

https://www.ads-software.com/plugins/all-in-one-wp-security-and-firewall/