That is probably because you were not progressed in the field upgrade to that point. You need to "level up" your field upgrades each time you play, and each time your entire squad is dead, you lose a level and have to keep leveling back up. The progress bar is just above your squad list by your map. The bar above the icons shows the progression. You progress by getting squad points like: squad revive, squad resupply, squad order followed, etc.
It does not work like Battlefield 3. In BF3, you would pick a "perk" and you (and your squad if you had the squad perk) would benefit from that, and you would be able to use it on any server.
However, they changed it in BF4. You now have the "field upgrades" which benefit you, and only you. You must level these up each time you join a server. The lowest of the 4 field upgrades will always be "unlocked" for you and benefit your soldier (and your soldier only). Your progress bar (above your squad list by the map) will progress when you get squad points such as squad revive, squad resupply, squad repair, ect (any points that say "squad" in front of them). Once your bar goes to the next field upgrade, you have unlocked it. You can keep progressing until it is full. Some of them wont activate immediately, it will the next time you spawn. I know one is weird, the vehicle resupply one, that will activate when you leave the vehicle and hop back in. Once your entire squad is dead, you will drop down to the last progression bar. So if you had 3 field upgrades, you will drop down to the second one. If you had 3 field upgrades and were almost to the 4th, you will loose all progress to that point and be down to the 3rd one again, so you only lost your progress to the 4th and didnt actually lose any field upgrades. If you decide to switch squads while on the same server, you will retain the field upgrades and progression on it, but not if you switch servers. The field upgrades will ONLY work if you are part of a squad, if you are not in a squad, then you dont receive them.
That sucks!
