The .cleverapps.io domains have issues resolving through multiple DNS servers. It seems like the top .io TLD DNS servers are the root cause of the problem. Users using this domain may have error messages like "Server not found".
If you need it, here is the IP of the domain: 188.8.131.52
EDIT 19:43 UTC: The incident seems to be resolved, .cleverapps.io domains now resolve correctly