If I don't include an offline wallet will it effect my cost basis

My Performance dashboard is definitely off because it says my net deposits are $27k and my own records show about half that. I’ve only traded on coinbase, coinbase pro, and my trezor hardware wallet. however, I had another trezor wallet that I sent coins to and from coinbase pro, but then I formatted that wallet when I thought it was hacked. As such, I didn’t add it to my cointracker account. Would that affect my reconciliation if that wallet has had activity but was not added to cointracker?

Yes: not having 100% of your cryptocurrency transactions across all exchanges and all off-exchange wallets can impact your cost basis. Please do your best to ensure all your transactions are accurately accounted for.