It is HIGHLY unlikely Nucle has been compromised, especially since it’s not even functional at this time.
The more probable likelihood is that since Nucle only uses individual wallet addresses. However as you move Chia around and make spends, coins get reallocated to new addresses within the same wallet… Addresses of which Nucle doesn’t support because the app has not been sufficiently updated since it was first deployed to support this functionality. If you take your seed phrase and load it into any other wallet, such as the Chia Network reference wallet, you’ll likely find all of your funds there because newer wallets that are kept up-to-date are able to see balances across all addresses derived from that wallet.