Intermitten lag on acceleration

I have a 2020 Chevrolet Spark with a little under 113,000 miles, most of them
highway miles.  I recently changed the air filter, then had a mechanic change
the plugs and serpentine belt.  Coil packs were not changed. A day after the
plug change, while at a light, I noticed what felt like a slight misfire, but no
check engine light came on and all other performance was fine.  In the two
weeks since then, I am noticing an infrequent, intermittent lag or "kickback"
when accelerating from a standstill or from a lower speed.  This might only
happen once or twice in a day of 90-100 miles of driving.  RPM's are normal,
fluid levels normal, no check engine lights, everything seems as it should
except for this occasional lag.  Any ideas?