This is interesting for debate on whether this is fair to students who have submitted their application on time. I'm all for support in having the 4th round, but I'd hope that decisions on that would've been made after 3rd round completion. Especially, after we waited so long already. 2020 is truly a variable year keeping us on our toes.
Bremners's guess is probably the most plausible explanation. I hope the rest of us Round 3-ers still get to hear by end of this week.