The MCU (MCU1) that came with the early Model X is the same as the MCU with which the 2012 Model S was built. The MCU1 were already relatively slow by the time v10 of the Tesla software was released (late 2017 or 2018), and they had a relatively small amount of storage (eMMC) on them, so that storage would slow down and fail over time as more data was used and more overwrites were performed. There was a TSB for a warranty upgrade of the eMMC that Tesla would only perform for free if the software detected failure in the eMMC (as opposed to performance problems), so many users opted o pay to upgrade to MCU2 instead. MCU2 has more storage and a faster processor, so it improves the user experience for these vehicles and also allows for new features that weren't included in the firmware for MCU1 models. If you can verify that you are running MCU1 and don't have the eMMC upgrade, this is a feasible culprit that will at least bring other improvements if it doesn't resolve the problem (and won't require a diagnostic fee, but does come at a cost). As such, it would be advisable to research MCU upgrade vs eMMC upgrade to determine which upgrade might be right for you.