GL.iNet GL-MT300N-V2 & LTE IPv6

I have a router GL-MT300N-V2 (fw 3.012) and there is an LTE modem Huawei E3372h in router mode (hilink).
LTE modem works perfectly through the SIM card with IPv4 and IPv6 networks. This is when you connect directly to the computer. But when it is connected via GL-MT300N-V2 in tethering mode all sites are opened only in IPv4 versions.
What’s wrong? What should I do?

Do nothing - it works and stick to IPV4.