Not sure if this has been discussed on any other threads related to this issue, but here are my observations from the following issue. When you are killed and the timer runs out only for you to be stuck staring at your death screen.
When this happens, it's usually after someone has built a fortification on my corpse before the respawn timer has finished. The only way to get released from this state is for the entire squad to wipe. You must get the squad wipe screen. Once that happens, you should be released and allowed to respawn. This has worked for my squad mates and myself 100% of the time. I hope this information helps someone.