I tried again with a 16GB USB flash drive, formatted FAT32, and copied the files from a Windows 10 machine. This time only the Windows Filesharing part died, meaning \\192.168.0.1 just gave an error....

@Tony I have parental controls enabled. It's not so much that it stalls, it's more that the router firmware seems to crash. Once it's gone down, I can't join the Wi-Fi network, nor access the Web UI....

@Tony I'm having the exact same issue with my AX50. Verbatim USB3 500GB drive. Formatted as exFAT. I found copying large files to it with SMB crashed it quite quickly. Copying to it over FTP seemed...