Sorry it didn't notify me about your last message, but yes you did as I suggested. I'm sorry it didn't work out.

Then it's going to be your add a wire's Y diode is connected into your Y and G wires. (I had a feeling that was the case, but never hurts to try something simple before digging in)

I'm out of my depth in troubleshooting the add a wire. So I'm hoping we can find what we need for a rewire.

It appears you have a 5 wire run between thermostat and furnace. I would pull off your thermostat and see if you can find the 'Y diode' and the brown wrapped wire bundle with 1 each of white, yellow, red, green, and blue. Don't be afraid to give a decent tug, and don't be surprised if it's a long line. (Mine is 4 feet.) Just keep going to you get stuck, or you find the brown bundle sleeve.

If you find it then you can remove the diode, and wire directly. Completely abandoning the add a wire. (You may have to move a few wires, and possibly modify your nest settings, but it's easy.)

If you can't find that bundle in your wall then you'll need to get a tech out. Just let them know you are having improper communication between the thermostat and furnace, suspect it's your add a wire, and can't figure it out. I don't believe you'll need a new wire run.

Add a wire is for exactly what it sounds like. It lets you add a wire, but they can be funky. Looks like someone pulled a 5 wire for the thermostat regardless.

The brown wire bundle that has the w1 connection goes to thermostat, the other with the unused blue and green goes outside to your AC. (Standard)

If you can find the blue wire behind your thermostat you can fully disconnect the add a wire, and connect as standard (recommended).

If not, it appears the add a wire isn't connected properly anyway, (appears to be missing diode) you could move green wire from your thermostat over to G (so both greens are in G, and see if that resolves. Note it looks like your add a wire was adding a c wire (white at thermostat, and also not an approved wiring by Venstar) so double check your still getting power with a multi meter between R and C behind thermostat (This is the funkiness of add a wires.)

Let me know what you do/find, and sorry about late reply bed time.

That is the correct place. It looks like the green wire from your thermostat goes to a blank spot between C and R

If you follow the white wire connected to W1 back to its bundle (thermostat bundle) you'll see the green wire from there goes to blank and is connected with a brown wire. I'm not 100% sure where that other green wire comes from. (I'm thinking AC because it's the same gauge and direction as R and Y1.)

It also appears your yellow thermostat wire doesn't connect to the board, but connects to something to the left. (I assume there is a wire nut just out of frame.)

If you recently had an inspection I would ask if he can come back because the system is "acting weird." When you engage just the fan. A lot of times they'll come back for free if you're polite, and it's something they should have caught.

If they are going to charge you something significant, and you're comfortable playing with your wires. I can see if I can help you rewire. (There are several wires I'm not sure about from this picture, and I don't want to say I can just yet, but it's highly likely, and if I'm out of my depth there are some actual HVAC people here who might be able to tell you how to correct. (I'm just a handy man.))

I'll just ask for basically the same picture just a bit farther out so I can see the wire runs (to make sure I know what's connected to what), a list of those ports order. (Kinda hard to read from photo especially around C and R.), and the wire plate of the nest. (So I can confirm what color in each port.)