DTPO 2 - Links not Working Consistently

I have a link in a rich text file in DTPO 2 that is not opening. I did a search, and I can actually locate the file. It resides in a group that is indexed. How can I get this solved? It has happened a couple of times.

Does the link work on the Mac? What URL does it link to?

Many of the links that are not opening are to OmniOutliner files. The files are in a group, which is similar to Dropbox, and which I have indexed in DTPO.

Screen captures or a screencast would be helpful.

And the actual links: Are they Dropbox links, DEVONthink item links, … Could you share an example URL?