I cannot tell what's the root cause in a simple word. But from the symptom you mentioned, it looks like the stack is corrupted after Uboot is relocated to SP=90000a60. So although the uboot prompt is showed, when you execute any uboot console commands, it messes up.
If you have a debugger such as DS-5 debugger, it may be easier to debug further. If you do not have, it may be a bit difficult. What I can suggest is to compare the SRAM content before relocation and the DDR content after the relocation, especially for the stack part.
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