Model : TD-W8970B

Hardware Version : V1

Firmware Version : 0.6.0 2.11 v000d.0 Build 150526 Rel.54651n

ISP :

So lately i have been having network stability issues with my two tp-link 8970B routers. the network is set up like this:
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Router1 (connected to internet) --wifi-- Router2 --lan-- pc
--lan-- laptop
--lan-- raspberry pi
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This setup has worked for me for a while now but during the last couple of weeks it has gotten almost impossible to download bigger files from the internet. whenever i start a download it will work just fine for a couple of minutes, but after about 10-30 minutes the speed will decrease to something around 10-50kbps, stay there for a minute or so before the connection breaks up entirely. now while all the clients and router2 say that they are still connected, I cant pull up router1s' webinterface or any other website. this will go on for maybe a minute or so when after that everything will start again from the top.
for the last couple of days i have connected the laptop via wifi directly to router1 without any problems, which makes me think that its some problem with the wifi-bridge. other things i have tried without making any kind of difference: resetting both routers, updating the firmware so they are both the same version, switching router1 for 2. also for the life of mine i cant think of anything i changed in the settings before the issues started. so yeah, i'm open to suggestions if anyone can help.