Are you still on MCU1, and if so, have you had the eMMC replaced? If you're still on MCU1 and have not have the eMMC memory recall done, then this could be a symptom of the eMMC memory chip starting to experience more issues.
I have a mid-2016 MS90D. I recall seeing over time it taking longer for the instrument panel to come alive versus the center screen became more common as more "quirks" of the aging memory chip started to pop up. I did have energy savings turned on, so expected some delay, but normally I'd open my rear door first to put in my backpack, and by the time I'd get in the drivers seat, buckled in, the IP would be alive. I did finally decide to bite the bullet and pay for the MCU2 upgrade in early December, so do not have recent experience of it becoming progressively worse.