But sometimes when I navigate into this menu (when the AC motor is either on or off), and very randomly, the LCD is "freezing" and after 2 seconds the display is reseted. The 3-phase PWM outputs are not affected at all.

Now, if I remove only the interrupts (TMR1_INT, INT0, INT2) of my program, this problem doesn't occur.
Do you get the fault indication? I suspect, you are getting into the FltSub when you say the LCD is frozen.

You can possibly disable the ocint and the stopint for checking this possibility. Does the LCD still freeze?