Hi Hydralisk. Unfortunately this is one of several bugs that were introduced with the latest update (1.1.0019.5). Several items, including the green ration packs, RG6 grenade launchers and VOG25 grenades (and probably other items that I have forgotten) now disappear when you change maps.
The only workaround that I know of is to spawn them in manually - but they will disappear again next time you change map, so only spawn them in when you need to use them (e.g. to hand in for a mission).
The RG6 and VOG grenades are in the main Spawn menu (ESC+S), but I don't think the ration packs are listed there. Fortunately you can use the ESC+F4 item spawn menu instead. Open the menu and type irp-b and click the SPAWN! button, and a ration pack should appear on the ground near you. If you want to spawn more than one, add a comma and the number - e.g. irp-b,5.