How you transfer the files?Generally speaking the wireless routers should be general used.

Have you changed a fixed channel on your main router? If yes but the same issue, it's better send email at support@tp-link.com to aks for further help with this issue.

Make sure your MAC computer connect to TL-WA855RE's wifi not your new router's. : Just press reset button for 1s to hard reset TL-WA855RE. : Then, try to login with admin/admin again.

It does not support via FTP, SSH or something like that. If you want to save all the camera recordings, it's recommended to add a NAS.

Can you check the data consumption of specific client on the router?How do you tell those data consumed by the camera? We'd better figure it out whether all those data are consumed by the camera...

Used as the RESET button: With the camera powered on, press and hold the WPS/RESET button for more than 5seconds until the System LED turns off. Then release the button and wait the camera to reset...