I got the file and isolated the issue. The error message is returned for the ‘1’ capability.
There is a strict type checking at the URE code:
if ($key!==$sanitized_key) {
But $key contains an integer 1, but $sanitized_key contains string ‘1’. So check is failed and returns error.
I see ‘1’ capability from time to time at different client sites, but still did not have information what plugin can add it. Try to revoke it from all roles to which it is granted. Then delete this capability as unused. Export roles again. This problem with import should gone away.
Thanks for pointing me on this issue. I will enhance a code here.