Azure Netx Duo Telnet Client stops receiving packages


Currently I use the EK-RA6M3 board with the Azure RTOS ThreadX and Azure RTOS NetX Duo Telnet Client to connect with an Telnet Server and to receive messages from it. 

This works, but after 6 messages (sent with an interval of 1 sec.), the Client doesn't seems to receive any new messages any more.

I checked the server side and I'am pretty sure that it is still sending messages to the client. Also when I connect with laptop+RealTerm instead of the EK-RA6M3 board, I received messages without any interuption or what ever...

My first thoughts were a buffer or queue what is getting full and it doesn't take any message any more but I tried many "increase-size" actions of buffers, but without any success...

I'm really have no idea what the issue is, and I hope someone could point me in a direction to search..

I use the E2 studio with the FSP v3.8.0 package configurator. 

If more information is needed, please let me know!

Thanks for any comments in advance!