The supernatural occurrences went off the hook once she accidentally returns back into her own body to the modern world. She could spiritually connect herself to the past in her sleep and be with ML. After returning back to the past things with the ancient cast finally settled and the royal strife over. Somehow MC and ML both ended up in the modern world again, to marry a third time.

Besides the lack of reasoning for all that back and forth transmigration, the ending is super generic. You've seen this in other novels before or as many many alternative TV drama show endings.
Also, with MC ending up with ML in her modern body, this bumps them also back to being a generic pretty boy X pretty girl couple *sigh*. So, the disparity of class, lookism and gender has also been minimized a whole bunch, making their efforts ending up together a lot less meaningful.