[1999 Lexus ES300] Slip Indicator (Squiggly Lines) Light?

A couple days ago after I pressed the gas pedal at a green light, the car started normally but at around 10-15 mph it seemed like it hard braked (stalled, jerked) for a second and then it ran normally.

Today, again after a green light at about 10-15 mph, it jerked twice in succession and I saw the traction light blink twice on the dashboard. Ref: https://dashboardsymbols.com/wp-content/uploads/2019/06/Stability-control-indicator.gif

I have checked transmission fluid and it's clear and full.
Other fluids are topped also.

What should I check next?

Few things to note:
Driving on dry surface. Has not rained here in months.
I press the gas paddle and accelerate slowly - not in a rush to go anywhere.