I don't see anything wrong in this sentences . So according to me it is ok and meaningful .

"During the party, the topic of our conversation somehow turned to our supervisor's girlfriend." You could also say, "During the party, we somehow started talking about our supervisor's girlfriend."

No. Any of these will do: During the party, the topic of our conversation somehow, WAS about our supervisor's girlfriend. During the party, the topic of our conversation WAS, SOMEHOW, about our supervisor's girlfriend.

We'd understand it, but it doesn't sound natural.