I am having the same issue on a Surface Pro 7 using the Microsoft Precision Mouse and the Surface Dial. Both drop out and the only solution is to restart.
I may have found a solution to my issue and it wasn't due to an update. I have found that my old SP4, which is in another room of the house, appears to have been causing the sporadic dropout issues. I wasn't using the SP4 and only using my SP7 until we moved recently. I set up the SP4 in another bedroom in the house and it must have been close enough that, every now and then, to grab ahold of the Surface Precision Mouse and the Surface Dial. Since removing both from the SP4, I have not had either drop out since.