DataFlash log viewer shows all th3e same numbers on X-axis

I've noticed over the past couple of months that sometimes when I zoom in on a log, all the X-axis line numbers becomes the same as shown above.

Start by reproducing the issue in the DataFlash log viewer: zoom into a log and observe whether all X-axis labels become identical, as shown in the screenshot. Trace the X-axis label rendering from the viewer entry point and verify that labels remain meaningful after zooming; no file or test is named in the issue.

Written by the indexing model from the issue text.