Lag or hesitation when accelerating from low speed or standstill

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.  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 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, everything seems as it should
except for this occasional lag.  Any ideas?