@Bobrock 

We will do some troubleshooting and locate this issue and try to fix it. 

May I know who is your ISP? What about the normal network activities, like web browsing? Do they have the same issue?

What is the light status of the C1200 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.

When the network stops working, are you still connected to the TP-Link wifi but no internet or it is disconnected totally? Please check the IP address and default gateway with your computer connected to the modem/router separately and show me the status-details page. Instruction as below: https://www.tp-link.com/support/faq/838/

At that time, please login to the web UI of the Archer C1200 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. 

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/

Below are some suggestions you can give it a go:

1. Customize the wireless settings of C1200 to optimize its performance, including wireless channel and channel width. 

2. Enable UPnP of the Archer C1200 under advanced-NAT forwarding.

3. Ensure that the firmware is up to date. 

Good day.