STM32F767ZI + lwip + FreeRTOS: no ping response / can not compile LwIP_HTTP_Server_Netconn_RTOS example

Dear all,
first I have to say that I am new to STM32F7 mirocontrollers, but I am not new to ARM-Cortex M4/M7 based controllers in general, nor the lwIP stack nor FreeRTOS.
I have the following two problems:
- SMT32F767ZI + lwIP + FreeRTOS: I tried to build a simple application using the lwIP+FreeRTOS (on a Nucleo-F767ZI board) using STM32CubeIDE (1.5.1). I set up a new project, configured my MCU and tried to ping my board. This, indeed, does not really work. There is a reply to the ping response, but it is a kind of "mysterious" data (a lot of 5s, which looks like a part of the synchronization sequenz of ethernet frame, but this should not be catched by Wireshark, see the attached file). I debugged the lwIP stack down to the point, where the response is sent and I have to say that even the data, which are referenced by the DMA transmit descriptors, seem to be OK (it is not the sequenz of the 5s, which is seen in Wireshark). Is there anybody, who has ever encountered such a problem? As PING packets are received and processed, I assume the basic configuration is OK. FreeRTOS and lwIP are included via the GUI (.ioc) file in STM32CubeIDE, the lwIP settings are nearly unchanged, the settings are: ICMP, TCP and UDP modules are enabled, checksum calculation is done by hardware.
- The second problem: I tried to set up my application on the LwIP_HTTP_Server_Netconn_RTOS example, imported into STM32CubeIDE workspace. But I can not build the example as a lot of files are missing (e.g. httpd_opts.h) and the directory structure of the example seems completely different than as it should be (e.g., there is no path "lwip/apps/httpd_opts.h). Does anybody know how to fix this problem (get the missing files)?
My application from the first question is configured like the LwIP_HTTP_Server_Netconn_RTOS example (MPU, fixed sections in memory), as far as I can reengineer it from the LwIP_HTTP_Server_Netconn_RTOS source files.
Kind regards and thank you for your help.
