TL;DR
The FIAT and BTC gains shown on the Realized and Unrealized Gains page can differ significantly. This is because CoinTracking calculates gains in BTC and FIAT independently, based on historical prices—not by converting one to the other.
Why BTC and FIAT Gains Can Differ
CoinTracking does not simply convert your FIAT gains into BTC or vice versa. Instead, each transaction is evaluated separately in both BTC and FIAT using the historical market price of BTC at the time of each trade.
Because of fluctuations in the Bitcoin price over time:
Your BTC gain can appear negative
While your FIAT gain is positive — or vice versa
This behavior is expected and accurately reflects how prices have changed over the holding period of each asset.