Electronic – One of ten 74HC595 shift registers have wrong output state when clocking in data

I have a project that uses 10x 74HC595 shift registers to control a series of electromagnets (80x magnets in total), switched with transistors. My current situation is that when I pull the reset-pin of the '595 LOW and HIGH again, and thereafter clock the latch-pin, the outputs of all the '595s change to LOW, as expected. However, as soon as I start clocking bits in, one of the '595's output pins is also miraculously HIGH, whereafter it also shifts a HIGH bit as it would normally. The only difference is, it should be shifting only zeroes until the HIGH bit reaches that shift register and gets shifted through that particular IC. For some reason and by some means, that particular '595 gets a HIGH bit in its register and shifts that out. I have checked the serial input pin just before shifting, and there is certainly no HIGH bit being shifted in from the previous '595. So I have no idea where that particular HIGH bit is coming from.

Attached is a snipped from the schematic of how the '595 is connected. The outputs are connected to NMOS transistor gates for controlling the electromagnets. Below is a snippet from the code that controls the '595s:

void main(void)
{
    int i;

    /* Reset the shift register contents and latch new contents */
    shiftReg_reset = LOW;
    delayus(1);
    shiftReg_reset = HIGH; //LOW-to-HIGH transition
    delayus(1);
    shiftReg_latch = HIGH; //Move new outputs (all zeroes) to latches
    delayus(1);
    shiftReg_latch = LOW; //HIGH-to-LOW transition
    delayus(1);

    shiftReg_out_en = LOW; /* Output enables '595s (active-LOW) */
    shiftReg_reset = HIGH; /* Pull reset pins HIGH (active-LOW) */

    for (i = 0[![enter image description here][1]][1]; i < 80; i++)
    {
        /* Set data pin */
        shiftReg_data = HIGH;
        delayus(1);

        /* shift bit */
        shiftReg_clock = HIGH;
        delayus(1);
        shiftReg_clock = LOW;        

        /* load '595 contents to output latches */
        delayus(1);
        shiftReg_latch = HIGH;
        delayus(1);
        shiftReg_latch = LOW;
        delayms(250);
    } /* for */
} /* main() */`

I have no idea what is causing this behavior. As you can see from the code, the shift registers' outputs are all zeroes initially, but once the second bit is shifted, it seems like the same bit gets shifted from another '595 in the sequence, giving the idea that there are two sets of shift registers being interfaced to which output the same data, instead of doing it in a cascaded manner.

I have not yet connected any of the electromagnets to the circuit. For each transistor/electromagnet, I have also put in an LED to indicate the state of the shift register output. I am seeing the described phenomenon on the LEDs, so the phenomenon cannot be due to any effect caused by switching the electromagnets…