Motorhead, I had the same symptoms and it was the soft close latch assembly.

Since you have replaced the latch assembly maybe you can try removing then replacing the fuses/relay of the system to maybe "reset" the system?

OP, yours I have no idea, sorry...it sounds a bit like mine which I resolved by partially disassembling the latch and jerry rigging a broken internal tab, but mine stopped working totally before I dug into it, not working intermittently like yours.

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04 X5 3.0i auto
03 X5 4.6is