To be honest, I'd look anywhere but your router for the problem - unless you know for sure that's where the problem lies? Can you beg/borrow/steal another one to see if it makes any difference? I'd suspect your PC/the line to your home/the exchange/your ISP before I suspected the router. Some things to consider, beyond trying a different router, might include getting your ISP to do a test on your line, and checking whether your ISP is throttling you because you've exceed your monthly download limit.
OnePlus 5T review: Hands-on