x-axis label references out of sync with data series

I have a spreadsheet to track COVID rates in several counties. One row for each day. I have an x-y line chart with the date on the x-axis and the case rate on the y-axis. Each month, I add more rows and extend the data series by selecting the chart, clicking "edit data references" and dragging the dot in the lower right of each colored column. Initially, the label references (date column) automatically extend along with the data series. Since July 12, this stopped working - the label references are not extending. (image 1) I tried adjusting this manually in format - axis - category - label reference, but the labels are listed as individual cells, one for each of my 900ish rows, instead of a series. Trying to edit that list gets stuck in the swirling pizza of death for a long time. (image 2) Any suggestions?