Log into the TP-Link device, and look at the status page, mainly the upstream and downstream channels. Normally all of them sould be locked and the value of power for downstream channels should be between -15dBmV and 15dBmV. If the value of power is not in that range, it means the line quality of that channel is not good. The value of power for upstream channels should be smaller than 50dBmV and the value would be between 30dBmV and 45dBmV normally. If the value of power is larger than 50dBmV, it means the line quality of that channel is not good. If there is 1 or more channels with bad line quality, the overall line quality may be bad.

The next thing to look at would be the system log or events logs. Look for any log that is categorized as a critical 3 error. The critical 3 errors is the modem telling you that there is a issue with the internet signal. You need to contact the internet service provider, talk to a level 2 technician (a level 1 will just see you have internet and say its not them). Inform them that you do have internet, but you have constant drops, and see numerous critical 3 errors and would like them to clear those out.

Some customers reported that the ISP will fix the issue on their end, other times they have sent a tech so how it is resolved will vary.