Give us screen shot from Status bar from TP-link. What kind of connection do you have from ISP? Do you have any login/password?

Yes, it's abnormal behaviour your repeater. You have to replace this specimen

Do you have latest firmware on TP-link?

I think that better idea will be repeater.

I can see that much TP-Link TD-W8951ND has problems with power supply. Power supply has a problem with the current efficiency. You have to use power supply with parameters 12V/1A or 12V/1.5A and then...

We don't know your ISP and his ADSL parameters (VPI, VCI etc.)