In the current period NextGen calculation, review the opening balances in the balance sheet workpapers.
Verify that they represent the rolled forward closing balances from the balance sheet workpapers in the prior period Classic calculation.
In the 1st period/year of using NextGen content, the balance sheet workpapers will have the opening balances in 1 row and the closing balances in another row. While it is acknowledged that this isn't ideal for presentation purposes, this won't happen when rolling forward the calculations into future years. It's a one-off occurrence as part of the transition to NextGen content.
You need to re-enter the opening balances for all Fixed Assets workpapers as a one-off. Please see Fixed assets opening balances.