Unexplained Skyrocket of 5G Home Internet Usage

The thing that jumps out at me is March and April usage are incredibly small.  Your May looks more typical of "moderate" usage for a month.  Less than 100 gig in a month is *very light* usage for a household that is streaming any kind of video.  Plenty of households can burn thru a terabyte or more per mouth. I personally suspect that the issue is that the TM was under-counting your usage totals for March and April.  It is well known that TM data-counting service was regularly going off-line and not accumulating correct totals.  I believe that has been largely resolved now, but I myself have observed weeks-at-a-time in the past where data usage was not being accumulated at all.