eqos(4) throughput

i have this problem with eqos(4) on a rk3566 board (orangepi 3b)
when there is enough RX traffic the TX sinks packets (not all the packets are transmitted)
this causes a max tcp uplink throughput of about 300mb/s
testing udp tx only will get to 900mbs+
testing with iperf -c <server> -u -b 700m -d
will show 25-30% of the tx packets lost
the 25-30 percent can be decreased slightly if i fiddle with dtb ethernet tx_delay but 19% is the best i could get

can somebody running 14+ on an rk356x board test this
on box1 
(server) iperf -s -u
on box2 rk356x (client)
iperf -c <server_ip> -b 700m -u -d
and check the packets lost by client send stream ?

the problem is the same on an official sbc image (debian)

thank you