Hi Julie!
We are having a similar problem with our store (www.joandjax.com). We were having a lot of problems with our pixel firing twice at checkout, and I could not resolve the problem so I removed the pixel entirely to see if I could isolate where the problem was coming from. We have no pixel in our preferences, theme.liquid, checkout.liquid, etc. yet we STILL have our pixel firing on our website. I have checked every possible app and integration I can think of and I still cannot find it. We do not have any of the apps you listed installed. Would love if you could take a look, as this has been a huge headache.
Thank you so much!
- Anna