I had this issue and it turned out to be my silly goose dynavin n6, which I threw out the window (well someone bought it and works well for that person on a non-dsp vehicle). Yes, the vehicle electronics would shutdown, but somehow the dynavin would wake up the amp and I'd find the orange light on the gear indicator back on. I installed an Android system and all has been good since. Disconnect your dynavin and observe from then on. Of course, it could be something else.

Good luck!

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'05 E53 X5 4.4i, '97 E39 528, '07 E92 335i, '16 F86 X6M.