I cannot open a PDF that appears in the results of a search. See attached video. The file exists (it showed up in the search results), and can be opened (you can see the preview in the top right corner), and this whole process (search+open) works fine in Windows Explorer.
When files have very long paths, Opus may opt to use the short versions of them (if enabled in the filesystem) to send to programs, as a workaround for path and command-line limits in Windows and third-party applications.
It looks like Synology are not generating short paths properly here. In particular, there is no file extension on the end of the name, which will likely confuse a lot of software. The names would usually resemble the main filenames as well, but it's not technically wrong for the names be completely random, as long as the extension is preserved (or truncated to 3 letters if it's longer).
If you turn on the Name and Path > Short Name column in Opus you can check what the short names are for the files. If they don't have extensions then that would confirm the issue.