Discovered this bug / unintended consequence last night while chaining monolith runs.
If you have a boss that has a “revives after 2 seconds” tag you can open the green portal (but not enter) after killing this mob the first time, then kill again. What happens is you get the prompt to reopen the world portal to end of time…
So if you go into the 1st portal and loot your chest you are now able to open a 2nd portal INSIDE end of time, go through it and get a 2nd reward chest.
Seems unintended and wanted to call it out just in case!