I have mentioned in other communications that FS Person Tools sometimes thinks there are no Sources when in fact there are some, maybe even many.
After every copy of one Source from FS to RM it seems to requery FS and regenerate the lists on both sides. That's mostly an annoying wait time and I can't think what potential problem that helps to avoid. As long as you're still working on the same person, I think we just hope that no one in FS is adding/deleting the sources for that person and the list originally queried remains. If someone were editing it, we might miss a Source (small error, low probability versus the amount of time wasted waiting for the requery). Suggestion: only requery FS if the RM user changed, added or deleted an FS source, otherwise work with the last list you retrieved from FS.
It has happened to me several times that the requery brings back zero results. If there were 22 before it didn't just gain or lose one or two, it got nothing. I wait, and wait, 15 or 30 or 60 seconds for the list to repopulate but nothing. It's exceedingly improbable that this is true and that something deleted all 22 Sources in the last few seconds. If I exit from Person Tools and go back to the RM Explorer and find that same person and click on the icon to start Person Tools from there it finds all 22 of them as expected and I can add the few I had not yet finished adding. Happens lots.
The second instance where I have seen this happen is not on a requery in the middle of moving sources from FS to RM - it is on the initial callup for a person I selected in the FS Person Tools from the list where RM tells me that FS has new information for some number of people. I was only able to prove this today (though long suspected) because some of the facts on a person were very specific and I wondered why there were no sources for them. So I jotted down the RINs, left Person Tools, went to RM Explorer, found those people and - lo and behold - there were sources, many sources, for these people. No idea why they didn't appear before. There were too many sources on several people for something in FS to have suddenly added them in the 10 seconds it took me to get back to that person and check again.
In this latter instance it happened for several people in a row, not all of whom were in the same family (so even less likely that some FS process or person was doing something to that same group at the same time). It is as though Person Tools gets "stuck" and no longer sees any Sources until I get out of it. If you can figure out what got stuck and fix that, then maybe an idea is to immediately requery anytime FS says no sources, or provide a button for the user to force a requery. That button might also be useful in the description above where I'm suggesting that you NOT automatically requery after every single copy of a source from FS to RM.