Card View Cards moving around in lanes

Hi all, I have a conundrum that has been wrecking my brain lately. We have a Smartsheet set up in card view that our on the road engineers use for there daily jobs. They know to work down the lane in order from start to finish and we in the office put the cards in the correct order for there most optimal journey. However recently the sheet seems to be randomly moving the cards around in the individual lanes and I cant for the life of me figure out why. Has anyone ever come up against this before?