Best mifi/hotspot for direct camera FTP transferring to clients

[Bettcherphoto]

Hello- I have been trying to hotspot my AT&T iPhone 12 pro to my R3/s and R5 with horrible outcomes. Connection works, then drops and then it's a 20 minute process to reconnect if at all. Does anyone use a MIFI or Hotspot with any reliability? What hardware would you recommend for use both domestically and internationally. I have even tried connecting to the Canon Mobile file transfer software (NOT camera connect) wirelessly and via lightning to USB-C with NO luck. Can easily connect to camera connect software but need to be able to send direct from cameras.
HELP!