The bedrolls are not stackable (that is a property set in the item template).
There are actually multiple numbered item templates for empty cups (not sure why). The ones I checked here all stack together, though, and after checking a few saves I couldn't fine one that had multiple empty cups that didn't stack.
If you have a save handy where this is an issue (such as when the screenshot was taken), please email supportdos2@larian.com with it (or a Dropbox or Google drive link, etc). If you are using any mods, also include a list of those enabled and/or the modsettings.lsx from your profile folder.
Each save is a folder in the '..\Documents\Larian Studios\Divinity Original Sin 2 Definitive Edition\PlayerProfiles\<ProfileName>\Savegames\Story' folder.
In Windows Explorer you can zip a file or folder by right clicking on it/them and selecting 'Send To | Compressed (zipped) Folder' (and similarly in OSX/Finder).
