Igniting praetorian gas

I used to be able to ignite praetorian gas with the CRISPR by just tapping it at the gas cloud. Lately (for the last year or so maybe) it doesn't seem to want to ignite, or it's just really finicky about it. Do I need a longer tap into the cloud, or to put sticky flames under the cloud, or is there a weird hitbox near the ground, or is it only ignitable during a certain timing, or what?