‘And they journeyed from Iyim (a shortening of Iye-abarim), and encamped in Dibon-gad. And they journeyed from Dibon-gad, and encamped in Almon-diblathaim. And they journeyed from Almon-diblathaim, and encamped in the mountains of Abarim, before Nebo. And they journeyed from the mountains of Abarim, and encamped in the plains of Moab by the Jordan opposite Jericho.'
This contrasts with Numbers 21:12-13; Numbers 21:18-20 which says, ‘From there they journeyed, and encamped in the valley of Zered. From there they journeyed, and encamped on the other side of the Arnon, which is in the wilderness, which comes out of the border of the Amorites -- and from the wilderness they journeyed to Mattanah, and from Mattanah to Nahaliel; and from Nahaliel to Bamoth; and from Bamoth to the valley that is in the field of Moab, to the top of Pisgah, which looks towards Jeshimon (or ‘down on the desert').'
The difference probably lies in the purpose of the descriptions. These in Numbers 33 refer to the places where they encamped and set up the Dwellingplace (or in the early part the old Tent of Meeting - Exodus 33:7-11). Anywhere were the Dwellingplace was set up was special. That is possibly one reason for this list in Numbers 33. It indicated the march of Yahweh and where He stayed. Those in Numbers 21 refer to sites of well known interest, which were not necessarily campsites. Alternately the change of Dibon to Dibon-gad (Dibon of Gad) may suggest that these in Numbers 33 were the new names given by the children of Israel as in Numbers 32:38. That would explain why unexpectedly there was not a single similar name.
(We must not make too much of these differences. The descriptions in chapter 21 only include two specific ‘place' names, Mattanah and Nahaliel (and this latter simply means ‘the valley of God'). Bamoth is ‘the heights', the river valley and mountain sites are general descriptions).