Why is no mention made of the reaction, of Balak’s officers who were accompanying Bilaam, to the talking donkey or the revelation of the angel?
Perhaps they were astounded, but the pasuk does not mention it, because it is not relevant to the narrative.
The Daas Z’keinim and Paneiach Raza write that the angel killed the officers who were traveling with Bilaam, which explains why no further mention is made of them. Rabbeinu Bechaye explains that they were traveling in front of Bilaam and therefore didn’t observe or hear the commotion and exchange between Bilaam, his donkey, and the angel. Alternatively, even if they were present, they weren’t on the same spiritual level as Bilaam, and they were unable to see or hear anything out of the ordinary. Rav Aharon Leib Shteinman suggests that even though they witnessed and heard the exchange, the officers didn’t reflect on the miraculous scene that they had witnessed and it made no impression on them to reconsider the propriety of their plans, so no reaction was mentioned on their part.
From:Parsha Potpourri Points to Ponder
R' Schwab in Maayan Beis Hasho'eva uses this question to answer two other questions (My summary looks long, but it's really pretty brief).
He is bothered how Chazal knew from the words כי הולך הוא (Bamidbar 22:22) that Bilaam was going out of a desire to curse Israel:
And his second question is why Hashem got upset with Bilaam for going, put an angel there to stop him, and then told him to go again!
Rabbi Schwab then points out that the escorts were with Bilaam both before and after the encounter with the angel, but seem to be absent at the encounter:
Rabbi Schwas explains as follows: Bilaam was only permitted to go in the first place for his own honor, and was not permitted to go with the desire to curse the Jews - Rashi to 22:20
But Bilaam ignored this caveat of the instructions to go, and instead went with excitement to curse Israel. He was so excited and personally invested in the mission that he actually sped ahead of the honor guard that was with him! Seeing that כי הולך הוא, that he was going alone, that he was excited to go curse the Jews, Hashem sent an angel to stop him. The angels instructions were not to turn around - the instructions were to go with the escort, meaning to go for the honor that they are according you and not for the sake of the mission itself.
So, the ministers were indeed not there, as Bilaam had sped ahead in his excitement. This itself was the reason that his going was problematic.