I have just had a quick nosey around and whilst I can't find a chart for it, from what I have read I can pretty much it is the wan to lan throughput (or lack of) which is causing the issue.
You need to either get rid of your tp link and use the shub as a router or buy a new router and keep the shub in modem mode. These things happen every now and again and you need to move with the times. If you would like a nudge in the right direction I would strongly recommend
this over everything else. Think of it as an investment for the next 5 years at a bargain price.