Diagnosis
USB 3.0 radio frequency interference with the 2.4GHz WiFi band, or the drive is drawing too much power.
How to Fix It
Use a USB 2.0 cable to connect the drive to the router's USB 3.0 port. This forces the connection to USB 2.0 specs, eliminating the RF interference. If you only have a USB 3.0 cable, wrap the middle of the cable several times with a ferrite core choke. Second, use a powered USB hub or a hard drive with its own external power supply.
If That Didn't Work
The file system may be incompatible or corrupted. The R7000 supports FAT32, NTFS, and HFS+. Reformat the drive to NTFS using a computer (this erases all data). Ensure you use 'Master Boot Record (MBR)' for partition style, not GPT.
Heads Up
Even when working, the R7000's USB read/write speeds are slow—typically 20-35 MB/s max. Do not use it for streaming high-bitrate media to multiple devices simultaneously.