I have updated a folder from within the music explorer. During this multiple files have been added today (2016-12-10) - see picture "mysql.png".
But even after restarting Helium there's no node in music explorer->Added date for this date - see picture "helium.png".
Windows 10 Pro x64
What if you collapse the Added date node and then press F5?
If you then expand the node again, it should have been force rebuilt.
Absolutely. I tried to reproduce this behaviour myself, unfortunately with no luck.
The date appeared correctly.
If you can find a reproduction pattern which always will generate this behavior, please report it as a support ticket so that we can analyse it further.