With the mysterious arrival of a stolen diamond, a forensic investigator goes on a quest to Siberia to uncover a decades-old international crime linked to her lost family

Great points above. Seems like an interesting idea, keep going with it!

The last draft of the logline still fails to create a clear connection between the crucial plot points. The event that starts her off on her journey (the inciting incident arrival of a diamond and journal) is not directly connected to the goal of her journey to Siberia (find the truth).

In what way is the arrival of a mysterious diamond and her brother's diary, an out of the ordinary and significant event that motivates her to need to do something?

Secondly what is the truth she must uncover in Siberia? What is her actual goal? What is it that the audience will want to see her achieve?

Lastly how is the diamond's and journal's arrival connected to the truth in Siberia? How do the former necessitate the later?

I get that her family is from Siberia, but maybe make that more clear?