In my experience this happens randomly after a longer session on a single server:

After choosing "Respawn" in the escape menu, which usually kills you, you are not able to respawn anywhere. Choosing to deploy anywhere closes the map for a split second, but then returns you back to the respawn map. From the short glimpse when the map closes, it seems that your character is still alive in the original location (eg. choosing "Respawn" did not actually kill you)

After a few attempts to respawn this way I always get disconnected from the server, so it may be connection related - like the server thinking you are still alive maybe so it does not allow you a respawn?