I also experienced this issue in a heavy lag situation. I was playing Coop 10 Escape from Altis with bots; was at a large airfield surrounded by two OpFor tanks and at least a half-dozen infantry, FPS was chugging at ~ 15. After a few deaths the button was disabled with the label "Respawn Disabled", despite the fact that I had 9990 respawns remaining. 3 hours of work to get to that airfield, all to waste.