This has been occurring with our instances, too, but was limited only with our AWS GoAnywhere appliance and we have operational and technical workarounds. However, this past month we now have similar, sporadic "banner" errors as described here with all other remote SFTP endpoints, so I am opening a WRC issue ticket on it. I'll disclose any relevant information toward remediation here.

Assign values to properties in the business process execution context. Someone will correct me if I am mistaken, but you need to also add that variable in the Rules General tab under Temporary Variables.

An observation from trying JWT on my REST endpoints that were tripping me up -- I previously had UseSession enabled and that appears to conflict with CSP and JWT handling. I understand that disabled is its default setting, but if it's enabled, well, you waste a bit of time wanting an access token.