My graph looks fine on screen, but when I print or export a layout, I see a little blip at the bottom of symbols where the error bar is shorter than the symbol.

If the error bar is shorter than the symbol, Prism omits the error bar. Or at least tries to. But sometimes a remnant remains, and appears only when you print or export. One way to work around this, of course, is to change the data so there is no error bar on those points. Another workaround is to plot only "up" or only "down" error bars. Prism does that fine, even when the error bars are tiny. It is only when you request that error bars be plotted both up and down, that these extra blips appear. We'll fix in release 4.02.