Blocks on rows 1 and 3 with contrast fine means the display powered up but never got initialised, so it’s sitting in its one-line power-on mode. Almost always the I2C address. Backpacks with a PCF8574A chip are at 0x3F, not 0x27, and from the outside they look identical. Run a scanner:

#include <Wire.h>
void setup() {
  Serial.begin(115200);
  Wire.begin(21, 22);
  for (uint8_t a = 1; a < 127; a++) {
    Wire.beginTransmission(a);
    if (Wire.endTransmission() == 0) Serial.printf("found 0x%02Xn", a);
  }
}
void loop() {}

Second thing for an ESP32: the backpack on 5V has its pull-ups to 5V, so SDA/SCL idle at 5V into a 3.3V chip. It usually works and it’s not great. Either power the backpack from 3.3V (some LCDs go faint at 3.3V) or remove the backpack’s pull-up resistors and add 4.7k to 3.3V, or put a small level shifter in between. For something on a cleanroom wall for years I’d do the level shifter.

Tyler has part of it. Each receiver input also has its own resistance to that side’s GND2 (the input impedance, around 96k for a 1/8 unit load device, more or less), and the bias network ties A and B toward one side’s isolated supply and ground. Each isolated side is floating, so it settles wherever those resistances and the leakage across the isolation barrier put it. The two GND2s drift toward each other through the bus wires themselves. On a 2 m bench with nothing injecting current, that’s close enough, so it works.

Over 300 m between buildings you get induced common-mode voltages and lightning transients. With nothing defining the common mode, one side can sit far outside the receiver’s range and the link gets flaky, or the isolation barrier takes surges it doesn’t need to.

Standard practice: run a third conductor as a signal reference, connect it to GND2 at each node through about 100 ohm to limit current if the grounds disagree, and earth the cable shield at one end only. Michael, that’s why you were taught three wires, it’s the right habit. Keep the bias on one end and termination at both ends as you have it.

That’s the problem. On the Zero, pin 1 is at the SD card end, but on the inner row. The pin you used, outer row at that corner, is pin 2, which is 5V. Count from there: pin 6 on the outer row is GND, pin 7 is on the inner row. If your red went to pin 2 and the rest followed the tutorial with the board mirrored, the DHT22 probably had 5V or GND on the wrong legs, which is why it got warm.

Ways to be sure next time: the solder pad for pin 1 is square, all the others are round. And on the Pi itself:

$ pinout          # comes with gpiozero, prints an ASCII map of your board
   3V3  (1) (2)  5V
 GPIO2  (3) (4)  5V
 GPIO3  (5) (6)  GND
 GPIO4  (7) (8)  GPIO14

So: VCC to pin 1 (3V3), DATA to pin 7 (which is GPIO4 in code), GND to pin 6. Use 3V3 for the DHT22, not 5V, so the data line stays at a level the Pi can take.

Whether the sensor survived: DHT22s are tougher than you’d think. Rewire, let it cool, try again. If it still says not found with the correct wiring, it’s dead, they’re cheap.