Hi,
I'm facing the same or a similar issue: I have lots of files (more than 100,000) I'm syncing. Now, I have the case that about 600 files have changed and 300 folders should be deleted. Now, when I run SyncToy it looks quite quickly for changes and afterward
starts to add actions for every file. After leaving it alone for some hours it hangs on "Adding an action for...". I restarted it at least 5 times, but it continues to hang at some file (not necessarily the same) after a while.
Internally, SyncToy is still working and after some time it finally starts copying the changed files. May be SyncToy does some time consuming stuff just between adding actions and copying files, that is not propagated through the UI?
I made a dump, if this helps to solve the problem.
Thanks!