Parshat בשלח discusses the great miracle of קריעת ים סוף. We learn that Hashem told the Angels in Heaven to stop rejoicing because His creation, the Egyptians, were drowning. This was not a time for celebration.
The של״ה הקודש asks that it's written that when רשעים fall, there is רינה, happiness. He answers that the Egyptians were not really completely evil because they did acknowledge Hashem's greatness at the ים סוף. The Pasuk says אנוסה מפני בני ישראל כי ה׳ נלחם להם במצרים, that we must run away from בני ישראל, because Hashem is fighting for them in מצרים.
We see many instances when even our enemies receive some merit because they recognize the G-d of Israel. This explains why the angels were not allowed to rejoice. Shabbat Shalom