Timeline Offset?

Somewhat recently (within the last 2 months, I think?) I've noticed that on my timeline in AE, if I position the playback indicator on, for example, the 10 second mark, it isn't actually on that tick mark, it's about 3/4ths of the way from the 29th frame mark before it. Towards the beginning of the timeline it's accurate, but as the timeline progresses it becomes more offset. It's like this for every frame/second marker, and results in the end of my timeline being off by a second or two, so I have to overextend my composition length in order to access the desired end frame (for an 18 second animation I need the composition time to be 18:02 to be able to see 18:00).

I'd almost think it's just my framerate, but if that were the case I should still be able to position my playback indicator accurately as I have in the past, I would think. Unless there is a setting I changed mistakenly, or just something I'm unaware of?

It's a fairly minor thing that I've been able to work around until now, but I'm soon going to have to combine several AE files into one and I'm worried this will become a hindrance.