My two cents:
- The wifi driver for this router is being actively worked on, I would install an updated version of that driver; have a look at the bottom of this thread: Pre-compiled updated mwlwifi drivers for stable releases
- If the problem persists, I would open an issue or join one of the already open issues at the official site for the driver: https://github.com/kaloz/mwlwifi/issues
What you are reporting is quite similar to what others have been commenting before.