Most likely when entering figures in TTX, you entered the wrong amount for "prior years deprecation" already taken.
Take a look at the 2020 (twenty twenty) IRS form 4562 that prints in landscape format, titled "Depreciation and Amortization Report". You need to add together the amounts in the "prior year depr" column and the "current year depr" column, to get the correct amount of prior year depreciation to enter on your 2020 tax return.
