Looking at the errorbars demo in gnuplot 6.0 in XUbuntu 24.04.
http://gnuplot.info/demo_6.0/errorbars.html
I can see that the data points leave a white space at the intersection with the bars (either vertical, horizontal or both).
This feature is reproduced in one of my script with terminal set to pdflatex. If errorbar is called with pointsize smaller than one then this annoying white space appears and eventually may interact with the end tips of the errorbar if the data point is not centered (ie if errorbars are not symmetrically place up/down or left/right the data point). The white space is more evident the smaller the point size, as if a white data point with point size 1 were always plotted underneath the point but above the errorbar.
This did not happen with gnuplot 5.4 even when the errorbars were placed behind the datapoint (for instance first plotting with errorbars pt -1 and then plotting with points).
Is there any way of returning to the behavior in 5.4?
This is intentional.
You can change the size of the gap with the command set pointintervalbox <size>, where <size> is in units of the current point size, and remove the gap with the command unset pointintervalbox.