Hey all, my apologies for this issue. We were testing some changes to Group Respawn in the midseason patch and intended to revert them, but I failed to undo an important element.
The bug we have right now is that if any hero could be Group Respawned, all heroes will be Group Respawned (on a given team - the bug doesn't affect the other team). This is bad, because it means your respawn time can be averaged several more times than intended, leading to the 20+ second respawn times players are talking about in this thread. If you see a longer black screen when respawning, that's caused by the bug. Fortunately Group Respawn is still disabled in Overtime, so at least this won't stack as some players in this thread have hypothesized.
We're working on a fix, but it won't be ready before the weekend.