Who says he didn’t sense it? Just because he didn’t spell it out load for you it doesn’t mean he didn’t pick it up. It was just insignificant in the situation. He only said it out loud in case of Luke to inform his TIE flight because it was relevant to the battle. Luke was a serious potential threat because of it.
We make fun of Ric being Captain Obvious in PT and spelling everything out loud, but it seems there are people here that actually need it.
He could have sensed it but the fact that would omit such a thing from Tarkin when the topic of her resisting the mind probe is improbable. Also it seems Vader was talking to himself when he said the Force was strong with Luke. The TIE Pilots wouldn’t even be able to appreciate how much an advantage being Force Sensitive could be in such a circumstance.
Just how would such a pointless information help Tarkin? The reason for her resistance to the probe is inconsequential and it wouldn’t change absolutely anything. If anyone had any skill to break her that way, it was Vader. He clearly couldn’t do it even if he knew she was force sensitive. Reporting the details and reason for his failure to Tarkin makes no difference or sense. Asking Tarkin for an advice on a matter (force) that he had no clue about (and which was actually Vader’s expertise) makes even less sense. Above all, in the end Tarkin had his own method that was inconsequential to the force.
Then why did Vader talk about the Force and mention Obi-Wan in the movie?
Because it those two cases it was a relevant information. A small fighter with force sensitive pilot was a threat (as proven later in the film) and Obi-Wan did actually infiltrate the Death Star. Whether Leia was force sensitive or not was absolutely irrelevant.