It wasn’t sarin. Sarin is highly toxic. The people touching the bodies and the clothes of the victims would all be dead if it were sarin.
The evidence available to neutral observers in Syria is consistent with phosgene in a warehouse hit by the Russians. It is possible that ISIS knew, the factions within the Syrian government knew, or that everyone forgot where the phosgene was in the years of war.
Reportedly, some 1st responders did die or were affected. 30 minutes after exposure, (give or take a bit depending on circumstances) the victims / clothing would be safe to touch. Look it up.