Asset Bundles not caching

Hey folks, I've tried searching the questions/answers here, as well as reading the Unity docs and several online resources, but I can't seem to find anything to help with my current issue.

Basically, we are using asset bundles for scenes in the game, using the Standalone Player. They download just fine and load into the game. However, we have frequently seen situations where the player will download all of the bundles, play the game for a bit, then log out and log back in. At that point the asset bundles are being re-downloaded in their entirety.

We have multiple players doing this at the same time, with one needing to re-download while another doesn't. So it's not an issue of the asset bundle version changing during the first play session. We've triple checked that situation in the database and both players are attempting to load/download the same version of the asset bundle, so it is rather baffling.

We track the current version of the asset bundle in a database, retrieve that version at the load screen of the game, then begin downloading the asset bundles using WWW.LoadFromCacheOrDownload using that version. It downloads the bundle correctly, but it seems as though it is sometimes being marked as a temporary cache item instead of a permanent cache item.

Is anyone familiar with any issue similar to this, or a means to check or specify which caching method should be used?

Any help would be greatly appreciated. Thank you.