When harvesting most countables, it says "()" after the name instead of the actual number. I think this bug was introduced within the last couple of versions if that helps. Most stuff is affected, but not all, it seems. For a specific example, I just picked up "Large Dwemer Plate Metal ()".
Elven Arrows works (split in two operations to get the count right)
Large Dwemer Plate Metal - no repro, see screenshot - will need a log from user to progress
Nexus bug report from RobinHood70