All the various parts of SOCOM have been operating in Syria for about 6-8 months according to this tweet from CJTFOIR.
I posted some pics of the ranger convoy the other day here. If you notice, they're big, scary and fly American flags. They were moving in a deliberate action to the city of Manbij to send a message to the Turkish Army (and Syrian government forces, but mostly the Turks) that "America's here, and we support the Kurds".
Since then, CJTFOIR has said that the Turkish Army is acting as an occupation force and will not participate in the liberation of Raqqa.
Reference this map
1. YPG (Kurdish) aligned Arab tribes. (also apparently some Marines and SOCOM)
2. Turkish Army
3. YPG
4. Syrian Government (with attached Russian SOF)
Blue Arrow: Direction of US Army Rangers deliberate movement
Red Arrows: Direction of Syrian Government w/ Russian SOF
The Turkish Army made a deliberate move towards Aleppo (Operation: Euphrates Shield) to prevent Kurds and their allies from having a 300mi continuous border with Turkey.
The Russians don't want the Kurds to take anymore, and don't want the Turks to get near Aleppo (where fighting between Syrian rebels and govt forces apparently is winding down).
The Americans don't want the Turks interfering with YPG (one the US's only reliable allies on the ground).
So, by all trying to assert control of Manbij, they might be able to force the other out of the area.