Quectel RM520N-GL speed issues in 5G

Hello Quectel! Please help me find a solution. I tried the modem on two routers and three firmware versions, MikroTik RBM33G (MT7621, ROS and OpenWrt) and Gl.Inet Beryl AX (MT7981, OpenWrt), on the USB3.0 bus. The problem is that the modem does not develop a download speed of more than 250-270 Mbps in conjunction with routers, and when connecting the modem directly to the computer, there is no speed limit. USB mode on RM520N-GL 3.2. The firmware everywhere indicates connection speeds of 5000 Mbps. The processor load of the routers does not exceed 40%. Maybe the problem is in the modem settings?

Just one possibility, but have you tried lower MTU settings, maybe in the 1350-byte range? Or, turning on any “MSS Fix” option available on the routers? 5G/LTE carriers usually don’t support a full 1500-byte frame, and if attached devices on the Ethernet or Wifi side are trying to use 1500, resulting packet fragmentation can cause reduced performance. Directly-attached computers using a QMI, MBIM, NDIS, etc. driver might be ending up with a proper MTU automatically.

that is the problem with that processor. you can try software offloading at the firewall settings of openwrt. me, i gave up on 7621 routers and built my router using mini pc using openwrt x86/64