Tried to search the forum on this but cannot seems to find the answers. Hopeful sifu here can help me out

Current setup
- Upgraded to 100mpbs with Archer C1200 router
- Firmware, flush to 20180208 EU version
- Use NAT boost. Disable QoS
- Disable WPS
- Disable ipv6

Issue 1:
No matter how I change the setting, I cannot get 100mpbs download from speedtest.net (with 2.4). Normally getting 30-40 mpbs only
Any special setting which I need to configure in this router to get the right speed?

Issue 2:
Cannot update the DDNS for no-ip. Save but it have a message prompt 'failed to update ddns'

Any guide on the above is much appreciated