Bug: old filenames of attachment links are displayed and won't be updated
I renamed many PDFs on my disk which broke tens of links to files (not embedded attachments) in Zotero. I selected the broken links one-by-one in Zotero, clicked on 'Locate...', and pointed to the correct files. Double-clicking on the linked items works fine now and Zotero restored the correct attachment icons, but the filenames displayed on the Zotero list (middle pane) and on the right pane are the old ones. 'Check database integrity' and restarting doesn't update the filenames. I suppose rebuilding the index might resolve this, but it seems there is a bug.
If you want to rename files that are in Zotero, you're much better off 1) letting Zotero rename them based on the parent metadata, 2) using the ZotFile plugin to choose a custom filename format based on the parent metadata, or 3) if you really want to spend time renaming everything by hand (which is generally not a great use of time), renaming them within Zotero by clicking on the attachment title in the right-hand pane and checking "Rename associated file", which will change both the attachment title and the filename.
I suppose it might make sense for Zotero to update the attachment title when relinking a missing file if the attachment title is equal to the previous filename, but when you rename things outside of Zotero you're breaking links, so it's really just not the right way to do things.