Xiaomi router 3g upload very slow

Hi, I have a Xiaomi R3G router with openwrt version: OpenWrt 19.07.1 r10911-c155900f66 and I have a problem that I can't solve (with previous versions of OpenWrt I had the exact same thing) upload is very very slow for me (it is normal that it works at 640mbs) and is running at 300-350mbs only, I have software and hardware acceleration enabled in firewall and it doesn't improve anything ... Can you help me? Is it a firmware problem? thanks.

The tests are performed by ethernet cable.