Inactivity timeout doesn't seem to be working

I'm running a pair of APMs on 12.1.2 and had the inactivity timeout set to 4 hours. I only have a few users currently connecting to these devices, but these sessions never seem to timeout. I had one user who was on vacation for a week while his laptop was at home, and he was never disconnected due to a timeout.

For testing, I had set the timeout value to 300 seconds and connected from my laptop. From there I put my laptop to sleep, and it didn't get disconnected for another 2 hours.

I'm guessing there must be a small trickle of traffic that is keeping the connection open, but you would think that when you put the device to sleep it would be enough to cause the inactivity timer to kick in.

Thanks!