@NuttyProfessor47, This may be related to the recent dimensional resolution change from 2 to 3 significant figures. Some users are reporting problems due to rounding after this change.

@andyfierman Quite possibly. Now I know the DRC minimum isn't really, I can compensate. The other issue I'm now having is a surfeit of hole sizes. By reference to the component data sheets I should need 8 hole sizes. In practice this could be rationalised down to 4 - e.g. components with wire sizes from 0.5 to 0.6mm could all use 0.9mm hole and 1.6mm pad. My Gerber drill file contains 15 different dril sizes, some of them only between 0.002mm and 0.01mm different. Are there ways to: a)  rationalise the hole/pad sizes used for component PCB footprints without recreating all my own personal clones of everything? b)  globally change groups of holes in the Gerber files?

(a) Not in EasyEDA. (b) The drill file is only a text file so you can edit that but unless you edit the rest of the files you could end up with pads having holes that are smaller then the inner copper diameter or pads where the drill hole takes out too much of the overall copper annulus. I don't know of any free Gerber editing software.

@andyfierman Thank you. I think I'll be updating the packages associated with components in my schematic and then "update PCB". Hopefully I'll then be able to tell whether the conversion to Gerber takes account of plating thickness when determining the drill size, or not, because I have already allowed for it in setting the hole size in the pad, and the pad size relative to it.