I have an Android app, called Guide Civilization VI. Under "Tips and Tricks", Gameplay, The Map, "The cost of movement", it describes queueing movement. I'm not absolutely sure Civ VI movement is implemented this way, but it is definitely how it was defined to work by Civ VI's designers.
For example, if the Scout has one MP left and you want it to climb an adjacent hill, right click on the scout and move the cursor over the desired hill (in the Scout's tile, there will be a circled 1 -- scout location end of this turn, and over the hill there will be a circled 2 -- scout location next turn) and release the right click to set your movement command. The Scout will not move this turn, but it will add the banked 1 MP from this turn and take 1 MP from its next turn, moving the Scout onto the hill with 2 MPs left! If you don't use your left over movement points in a queued movement command you will definitely lose any left-over MPs.
So queuing Scout movement even longer can result in what appears to be erratic movement, if one doesn't understand how queued movement works in Civ VI. For example, a Scout moving over a long sequence of hilly terrain will alternate moving 1 hill (uses first 2 of 3 MPs) and then 2 hills (uses 1 banked MP + 3 current MPs) and then the cycle repeats.
So, assuming one doesn't understand queued movement in Civ VI, and the Scout is one of the few units with 3 MPs, only the Scout would seem to move erratically.