I am in contact with SR regarding this issue. Got the following Information: "You are using the older revision 1.2 of the Hummingboard2 carrier. This revision is known to have issues with its boot select headers. Boot select is not reliable unless you fuse the SoC itself. Have you fused the SoC boot select fuses?" Probably this helps. I am not sure, if I fused my board. I Will check this next.
I am writing to confirm the behavior Igor has encountered. With my "old" hummingboard2 it is exactly the same. It is not running the u-boot image from SolidRun. It stops at "!MMC partition switch failed". I am loading u-boot from SD I think, because older images from SolidRun can be loaded correctly with the board, If flashing them on a SD card. I will follow this thread and contribute if there is something to check or test.