Nintendo Switch Online w/ Arcadyan KVD21 Router

So i’ve had this problem for over half a year now and it’s still really bothering me how I try to play online on smash bros and mario kart and i always get the same couple of errors, here’s one, “Error Code: 2618-0521
The server is operating normally.
The NAT traversal process may have failed.
Intenta nuevamente más tarde. If the problem persists, your network conditions may not be suited to stable
online play. Internet speeds, gaming and streaming are all fine but it just does not work on my nintendo.

Does anyone have a solution to this?