In init.bsh I get the AlbumObjectProperties of a folder's representing image. I then make a new image and put its width and height to the vars map and put the updated vars map to the object's properties. Later on I read the width and height using ao.getVars().get("width").

It all works, until in init.bsh I throw an 'OperationAbortedException' for an unsupported file being in the project. Having excluded or removed the offending file, when I do a make album the saved properties are now reported as null. To make the project again I need to reload it.

It is very repeatable.

Are you calling .save() on the AlbumObjectProperties after changing its properties?

(There are two variants, save() and save(boolean). save() preserves the last modified date and save(boolean) lets you decide whether to preserve the last modified date or not.

Yes, I used .save().

I have deleted jAlbum and downloaded it again, did a core update to get to 24.1.1 and then a beta core update (texts properties). It is now working as it should, so I've marked it as answered.