According to the earlier narrative(Numbers 10:14-25) the order of setting out of the tribes of Israel was arranged this way:
1)Standard of Judah
2)Gershonites and Merarites-carried Tabernacle
3)Standard of Reuben
4)Kohathites-carried the Ark of the covenant
5)Standard of Ephraim
6)Standard of Dan
But in verse 33 it is said that the Ark was leading when they went in search of a place to rest instead of the standard of Judah which was the norm
Numbers 10:33 NIV
33 So they set out from the mountain of the Lord and traveled for three days. The ark of the covenant of the Lord went before them during those three days to find them a place to rest.
Did they switch positions?