“D” disengages

To start I drive a 2013 Mazda 3. While driving the
vehicle the “D” on the dashboard will disappear
and when it does the vehicles engine seems to
disengage and the vehicle will lose speed. I’ve
brought the vehicle to two different garages and no
one can tell me what the problem was, but
recommended me to go through Mazda. I’ve been
to Mazda twice already and they can’t tell me what
the issue is, what’s wrong or they can’t replicate
the issue. It’s happening again and this will be my
third time. I’m hoping someone knows something
about this, so when I bring it to Mazda I can tell
them what to fix. Or does anyone recommend take
it back to Mazda and then if it can’t be fixed go
through lemon law? Any assistance would greatly
be appreciated.