The legacy Bittrex v1 API has been deprecated, if you're currently using the v1 API your transactions will no longer sync with CoinTracker. This article explains how to complete this simple migration to the v2 API.
Open the wallets page and click on your Bittrex wallet:

When the Bittrex wallet loads you will see the following prompt. Go ahead and click the "Migrate now" button.

After the migration completes you will need to remove the old Bittrex wallet so you don't have duplicate transactions in your account. On the wallets page, select the 'Bittrex (deprecated)' wallet, tap the dropdown arrow, and choose 'Remove exchange.'

Congratulations, you have successfully migrated your v1 API key to the Bittrex v2 API.