Different regions and carriers use specific modem firmware versions that can affect performance:
ZTE MF286D Firmware Guide: Updates, Custom ROMs, and Optimization zte mf286d firmware
: If already running OpenWrt, use a "Sysupgrade" image through the Backup/Flash Firmware menu in the LuCI web interface. OpenWrt Forum Troubleshooting & Tips [OpenWrt Wiki] ZTE MF286D Different regions and carriers use specific modem firmware