Move function not working under certain conditions

[DilithiumHydroxide]

This might be a bit convoluted so bear with me. I have 4 2 axis robots moving on a grid - so X and Y in both directions at any point. To move said bots, I have a function, move().

    def move(self, *targets, speed=100):
        # targets: XY target absolute position (Unit: grid tooth pitch)
        # speed: speed[%]

        assert len(targets) == self.vehicle_count * 2, "The number of targets does not match the number of vehicles"

        # Raise error if speed is out of valid range
        if not (1 <= speed <= 100):
            raise ValueError("Speed must be between 1 and 100")

        # Convert target coordinates from grid pitch to motor angle in degrees
        target_x_deg = [0] + [targets[i] * GEAR_RATIO for i in range(0, len(targets), 2)]
        target_y_deg = [0] + [targets[i] * GEAR_RATIO for i in range(1, len(targets), 2)]

        x_dist = [0] * (self.vehicle_count + 1)  # X-axis distances to target
        y_dist = [0] * (self.vehicle_count + 1)  # Y-axis distances to target
        x_step = [0] * (self.vehicle_count + 1)  # X-axis step sizes
        y_step = [0] * (self.vehicle_count + 1)  # Y-axis step sizes

        # Calculate distances from current position to target
        for i in range(1, self.vehicle_count + 1):
            x_dist[i] = abs(target_x_deg[i] - self.current_x[i])
            y_dist[i] = abs(target_y_deg[i] - self.current_y[i])

        # Calculate movement duration based on max distance and speed
        velo = MAX_MOTOR_ROT_SPEED * speed * 0.01
        max_dist = max(x_dist[1:] + y_dist[1:])
        time = max_dist / velo * 1000  # [ms]

        if time > 4:
            self.global_time += time

            # Determine number of steps
            step_num = int(time * 0.25)

            # Calculate step size for each vehicle
            for i in range(1, self.vehicle_count + 1):
                x_step[i] = x_dist[i] / step_num
                y_step[i] = y_dist[i] / step_num

            # Perform stepwise movement
            while step_num > 0:
                for i in range(1, self.vehicle_count + 1):
                    if self.current_x[i] < target_x_deg[i]:
                        self.current_x[i] += x_step[i]
                    elif self.current_x[i] > target_x_deg[i]:
                        self.current_x[i] -= x_step[i]

                    if self.current_y[i] < target_y_deg[i]:
                        self.current_y[i] += y_step[i]
                    elif self.current_y[i] > target_y_deg[i]:
                        self.current_y[i] -= y_step[i]

                # Track the position of the controlled vehicle
                self.x_motor.track_target(self.current_x[self.vehicle_id])
                self.y_motor.track_target(self.current_y[self.vehicle_id])

                step_num -= 1

Using it looks like this:

mvc.move(70, 10,  30, 0,  0, 10,   10, 0,)

Each of the coordinate pairs corresponds to one of the four robots, and depending on what the ID is set to (line at the top of the script), it will move the robot to the first pair, etc.

This works fine in most conditions, but for whatever reason, when the robot is at either 50, 0 or 50, 10 and I try to move it to 50, 10 or 50, 0, the robot moves at around at 1/4 the speed it should be moving, and for no apparent reason (even when I explicitly set the speed to 100). Is there anything that could be causing this?

Note: this code is not mine, so there may just be something I'm not understanding. If anything else is needed for clarification, please let me know!

(thanks dlech for editing the code so it doesn't look goofy - I'm new to GitHub lol)

EDIT: Strangely, it only happens when the robot ID is 1 - swapping between 50,10 and 50,0 for the 2nd set of coordinates has no issue
EDIT 2: Tested the EXACT same set of movement commands before the robot tries the 50,10 and 50,0 swaps, and on multiple robots. No matter the hardware, when the coordinates are in slot 1, it moves slower.
EDIT 3: the entire script is here at cfg_05 https://github.com/akiyuki-k/OmniDirectionalVehicle