Negative R squared in IV regression

Good afternoon everyone,

I am running an instrumental variable regression for panel data with the command xtivreg2 and everything looks fine: the Kleibergen-Paap and Hansen statistics indicate that the model is not underidentified and that the instruments are valid. My only concern is that the R squared is negative in some specifications (not in all of them).

I have read that a negative R squared is not necessarily problematic in IV, but it might be a signal that the model is misspecified. My question is, can I just ignore the negative R squared since my Kleibergen-Paap and Hansen tests are OK?

Thanks for your help