Has it been happening all winter also? Coz now a days in year area nights will be relatively cold. Might be the CNG reducer kit getting cold/freeze issue during constant driving in cold season.
Also the rpm issue arises frequently in civics, like, after refilling, after driving a little longer on petrol, after filter gets dirtier, after car wash, during long route, in cold weather, etc. etc.
Remedy I do is the slight adjustment of sensitivity knob on the cng kit, usually called idle set knob or whatever.