Over the weekend, a US military patrol in northeastern Syria was blocked by the Russian military and forced to turn backto where they came from. The US reportedly violated existing security deals with Russia.
Video of the brief encounter published by the Russian side shows the tense moment that Russian troops physically blocked the road while clutching their rifles:
The US and Russia both have troops in reasonably close proximity in Syria, and the US tends to hype confrontations heavily. To try to reduce the number of issues, they've made several deals to coordinate their patrols and avoid running into one another.
That works well, as far as it goes, but in this case the US didn't inform Russia ahead of time, so when the Russian forces ran into them, they complained about the US ignoring protocol on prior notice.
The US has not commented on why they ignored the protocol, but it's not clear why they bother to patrol anyhow, since the US presence is very limited, a hold-over from President Trump's plan to take Syria's oil.
Patrolling into adjoining Kurdish areas means the US retains some ties to the Kurds, but with Russia and Turkey also in the area, it's a potentially complicated matter, especially if the US considers previous deals to be optional.