Volume Number Metadata
I know this one is probably nitpicking, but would you mind setting the meta data on all large series to have leading zeros on volumes 1-9 so they sort correctly? It's likely known when a new series is licensed that it's going to hit this threshold, and it's not even a bad policy to have in your normal process to just do it for all series so the issue isn't run into anymore.
In my JNC library I have both Demon King Daimaou and Lazy Dungeon Master showing as 1, 11, 12, 13, 2, etc. It gets even worse when I pull the epubs into my own reader since I have to set the meta data on almost every series that is more than 9 volumes so it sorts correctly. And there are a number of current JNC series approaching double digit volumes...
As an add to the above, for series that include ".5" volumes, this also breaks pretty badly.
For me, I have to do things like "fix" all the metadata to be something like "vv.s" - e.g. 01.0, 01.5, 02.0, etc.
Honestly, I wish readers and libraries would actually sort these properly. Something like C#'s Version class which properly deals with the xx.yy.zz.aa version string (and its sub-variants, eg. xx.yy, xx.yy.zz).