Network functionality in v2020.04 on Raspberry Pi 4

[Jevtic, Sasha]

Hello all,

I am encountering considerable difficulty with the networking functionality on Raspberry Pi 4 on the latest release (2020.04).  In particular, I have observed:

    * any network operation that fails renders networking functionality inoperable until reboot.
    * ping always fails.
    * TFTP download attempt of non-existent file fails (resulting in subsequent network operations failing).
    * TFTP download of an existing file usually works, but occasionally experiences timeouts during transfers; some are timeouts are intermittent (the transfer ultimately resumes), and some are permanent.
    * TFTP download of a script usually works (as above). The script will run, but any additional TFTP downloads performed by a script all fail.

It is not entirely clear right now whether this is a problem in U-Boot (i.e., instead of in the execution environment set up by the Raspberry Pi firmware), but the TFTP infrastructure I am using is known to work well with other hardware running an older version of U-Boot.  Also, there are also no network issues in the Linux environment that I ultimately boot, so hardware also seems unlikely.  Thus, suggestions for things to check would be appreciated; I am of course also happy to provide any supporting data required to investigate.

Please also be aware that I initially posted a very similar inquiry to the Raspberry Pi Forum:

https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=271068

Thanks.

Sasha