2013 Mazda3 2.0 Skyactiv, auto, fwd; no OBD2 codes

Today I was slowing down exiting an inclined freeway offramp. I was only going maybe 15mph and was soft braking when I hit a small bump in the road and I immediately felt the brakes give out for a moment (the pedal dropped) before getting soft re-engagement. I continued to have very weak brakes the rest of the 3-mile drive home (needed to press brake pedal deep to get decent braking power) - I suspect the front brakes were not engaging at all.

After parking it at home for a bit and deciding if I should go straight to the mechanic, I decided to go for a test drive in the neighborhood. When I pressed the brake pedal to start the car, the pedal dropped all the way down, then it engaged normally on a second press. From then, the brakes seem to feel and operate normally - I drove around the neighborhood, braking several times and everything seemed normal again.

Background info: About a year ago basically the same thing happened (hit bump, lost brakes) but in that incident I was braking harder at a higher speed when I hit the bump. In that case the weak brakes continued after (instead of going back to normal like this time), so I brought it to a mechanic. They diagnosed a bad master cylinder, replaced it, and everything has been fine until today's incident.

Is it highly likely that the master cyclinder (or something else) is faulty again or is there another possible explanation within normal functionality? OBD2 scan does not show any codes.