Firstly, refer to the 4G router’s system log and locate the Wi-Fi device.
Then, access its control panel and try to upgrade its system or firmware.
After that, verify its Wi-Fi settings. Ensure to use the exact same Encryption type.
If it does not support the encryption type used on the 4G router Wi-Fi, then change the 4G router Wi-Fi to a paired type supported by the device.
Remember to reboot the 4G router and the target device after re-configuring the Wi-Fi settings.
Finally, if the issue still happens after configuring the above steps, try to turn off WMM mode on the 4G router Wi-Fi.
How to turn off WMM Mode?
WMM, Wi-Fi Multimedia, prioritizes network traffic to improve the performance of various network applications. Turning off WMM will slow down the speed but could give better support to legacy Wi-Fi devices.
Navigate to “Network > Wireless” after logging into the 4G router.
Click the “Edit” button on the master Wi-Fi hotspot to which the Wi-Fi devices connect.
Scroll down to the section “Interface Configuration” and unselect the check box of “WMM Mode.”