Outlets that seem to be on same circuit, but not behaving that way
The old way of running kitchen plugs was to split the top and bottom plugs so each plug was on a seperate feed. This was accomplished by running 3 wire between the plugs and removing the breaker tabs, the entire thing was conected to a dual pole break so the entire plug would trip at once.

If your house was built to code before the advent of gfci this is probably what is going on.

If you test the breakers for those plugs and find them tied together with breaker bars or some othe way this is almost certainly the case.

Unless they were wired with 12g cable you will need dual pole 15a gfci breakers rather than 20a gfci plugs to add gfci protection or to run new cable and 20a breakers.

Fyi: not an electrician