This is an issue that has plagued me a second time now. Seemingly spontaneously my main PC - connected to a node via ethernet - will have complete nothing download speeds. 

Very similar to this issue:

https://community.tp-link.com/us/home/forum/topic/664696?moduleId=2424

Previously I was able to swap the main Deco and that fixed the issue. However, the issue has returned and swapping the main Deco did NOT fix the issue.