Iperf3 client reporting zero data even though the server is receiving traffic

Hi,
I'm trying to do some throughput measurements, I sometimes get 0.00 on the Transfer and Bitrate fields like the following

On the server side I run the following command
`iperf3 -s`

On the client side I run the following command:
`iperf3 -c 10.0.12.1 -t 30`

On the client side:

Is is what I receive on the server:

When I set the TCP -w 64k window, there is no transfer 0.0.0, but if I try to extend it to w -128k, it appears again
`iperf3 -c 10.0.12.1 -t 30 -w 64k `

Is is what I receive on the server:

If I decrease the packet size -l 1k , or -l 10k this also happens
`iperf3 -c 10.0.12.1 -t 30 -l 1k`

Can anyone help me locate where the problem is? Before reducing the window, I would like to enlarge it, but 0 transfers are displayed, using UDP this does not happen.