Lock up

A constricted front rubber flex hose was a good suspect, but since those have been replaced already, look at the adjustment of the brake light switch to see if it is holding the brake pedal down a little.

You have already covered the typical stuff, so we have to look deeper. Besides the brake light switch, a lot of import cars use an adjustable push rod on the power brake booster. When locking brakes occur after replacing the booster or the master cylinder, that adjustment becomes a suspect.

We also have to consider brake fluid contaminated with a petroleum product like engine oil, transmission fluid, power steering fluid, or penetrating oil. Those will cause rubber parts to swell, and if any part with rubber in it is not replaced, the contamination will leach out of it and re-contaminate the new parts.

When this happens again, stop on a slight incline, shift to "neutral" place a block about a foot downhill of a tire, then loosen the steel lines at the master cylinder. If that does not make the brakes release, try opening the bleeder screws on the front calipers. The goal is to open the hydraulic system at various places to see where the brake fluid is being trapped.