Stem only collects mechanical royalties on US digital downloads and doesn't currently payout these royalties to anyone other than the content owner (hence why the composition splits will always be 100% to the uploader). You'll want to work with SoundExchange/PROs/pubs to fully collect on publishing splits.
These royalties are eligible to be paid to the uploader every 15th of the month.
We do not charge a distribution fee on composition earnings.
Stem does not currently visualize composition earnings in our dashboard -- we only visualize data from the sound recording earnings.