I’m not sure if the OP said he’s using erg mode or not. I could see that possibly causing a big difference in Power inside versus outside. I don’t have erg mode myself (so this is just a guess) but to me it almost seems like it would be easier mentally to not have to think about what gear you’re in while indoors.
I personally never used erg mode and have never had an inside vs outside discrepancy, only when using different power meters.