We have noticed a strange issue with Ymodem where the transfer sometimes stalls on the 1st attempt after typing loady and does not resume so you have to click Cancel on the Ymodem transfer in the Teraterm application for Windows. Sometimes u-boot remains waiting for a file and in that case we start the transfer again in Teraterm and the transfer almost always completes.
With small files that is an annoyance but not a problem. However with large files, we've noticed that the second attempt at transfer completes but has the wrong filesize (0x007f458a rather than 0x007f458d).
Do you have any ideas about this?