Disable(uncheck) Platform access wait for a few minutes and then re-enable.
What is the Hik-Connect version on your smartphone? Latest version seems to be 6.8.500.0403 for Android devices.
Check the primary and secondary DNS on your NVR. This should be 8.8.8.8 and 8.8.4.4. You could also try as primary DNS, the one of your dsl router Gateway that could be 192.168.1.1 or similar