For now there is only one known incident of use of chemical weapons in Khan Sheikhoun . Before, the US has blamed the governmental forces for the attack, but now it admits that the terrorist organisation Jabhat al-Nusrah operates in the region and uses chemical weapons against civilians. Hence, the US wasted money with its missile strike on Shayrat Airbase.
Recurring disinformation around the Khan Sheikhoun chemical attack. The articles refer to the Department of State Syria travel warning that states: Tactics of ISIS, Hayat Tahrir al-Sham (dominated by al-Qa’ida affiliate Jabhat al-Nusrah, a designated Foreign Terrorist Organization) and other violent extremist groups include the use of suicide bombers, kidnapping, small and heavy arms, improvised explosive devices, and chemical weapons. They have targeted major city centers, road checkpoints, border crossings, government buildings, shopping areas, and open spaces, in Damascus, Aleppo, Hamah, Dara, Homs, Idlib, and Dayr al-Zawr provinces.
The travel warning doesn't link the Khan Sheikhoun chemical attack and the use of chemical weapons by Jabhat al-Nusrah.
Further debunking by the Insider.