@aus_fas 

We will do some troubleshooting first and try to fix it. 

For the cloud server error, it is suggested to change different NTP server and correct the time settings of the C5400 to give it a go. 

For the unstable connection issue:

1. What is the light status of the C5400 when the connection drops out? Can you get internet from it via wired cable at that time? Please connect your device to the modem directly to do a comparison test as well.

Note: Please check the IP address and default gateway with your devices connected to the modem/router separately and show me the status-details page. 

https://www.tp-link.com/support/faq/838/

2. At that time, please login to the web UI of the Archer C5400 and take a full screenshot of the Advanced-status page; and go to advanced-system tools-system log  to save and export it to us. 

3. Besides, please follow the instruction below to do some test and tell me which case you belong to.

https://www.tp-link.com/support/faq/2237/

@aus_fas same issue here 

@zackattack784 

Hello, you can try to do some troubleshoot as mentioned above and tell us the corresponding results. 

And please show us what the current problem is and tell us the current hardware and firmware version of the Archer C5400 so that we can do further analysis. 

Good day. 

@Kevin_Z see this thread. 
https://community.tp-link.com/en/home/forum/topic/167404?page=2

@Kevin_Z 

Hi, I was provided beta Firmware by the support team (1.2.4 Build 20180525 rel.55808(5553)) that was significanlty better than the actual one. WAN_LED and all info from the log points to service restart after 4 days compared to after everyfew hour.

There seems to be issue with DDNS as well I think , so I disable that too.

Just recived a message for  a new firmware today for 1.2.5 Build 20190411 rel.52981.

Will try to see if that is better or not.