in general for troubleshooting steps you should first start with the below after confirming your hardware is set to support the right speeds :
Share how much you’re getting with multi-thread test (-P 12), what driver, firmware versions you have. and if there any drops reported by our nic on the Receiver ?
Driver and Firmware version : ethtool -i ethX
ethtool stats, preferable after the OS came after boot. capture from the receiver : ethtool -S ethX | egrep ‘drop|err|sto|paus’