The bug

The world is visible for a short moment after the credits but before you have respawned.

Code analysis

Based on 1.11.2 decompiled using MCP 9.35 rc1

The method net.minecraft.client.gui.GuiWinGame.sendRespawnPacket() resets the currently displayed GUI. But the player is not teleported until it receives the packets from the server.

Suggested would be to not clear the displayed GUI but mark that the player reached the end of the credits and therefor not send multiple respawn packets and not try to scroll further.
However, this might cause problems when the server does not send a packet back for whatever reason.