This also happens when trying to use “Other Roles” as well.
There seems to be a conflict with the Redis Object Cache plugin (by Till Krüss) as well. We cannot add users while both the Redis and URE plugins are active, and attempting to change the capabilities across the network is painful (constantly flushing the object cache across all sites) or just doesn’t work.
This is also the case on a completely different multisite on a completely different server that doesn’t use the Redis plugin, it uses SiteGround’s own plugin and caching configuration.
