WordPress Membership Plugin
We are having a similar issue when members try to update their profiles. And yes, we are using the Membership Form Builder add-on. We are NOT using any kind of caching.
Site: https://www.wb5rdd.org/
If someone tries to update anything in their profile they are shown this message:
Error! Security check failed for membership level identifier validation.
The submitted membership level data does not match.
If you are using caching please empty the cache data and try again.
If you are using the Form Builder addon, please update the addon and try again.