Doppler- Heart Beat 10 weeks

Sunday (9+6) I found babies heart beat on the Doppler at home.

Monday my OB found it (10 weeks).

I tried finding it tonight but couldn’t. I tried and tried for quite a while. There was one point where I thought I heard it.. but it only last a few seconds. It sounded like it was behind something.

Has anyone ever had this happen? Where you were able to find it once and not again?