You just copy and pasted a whole bunch of polylines which should have elevations 86, 87, 88, etc. but you snapped to something at 0 and now they have elevations 0, 1, 2, etc. Don’t go crazy trying to fix them all manually, just select the perpetrators and use MOVE, select the one that is at 0 as a base point and move to @0,0,86 (or whatever vertical increment they are off) and they will all shift happily up to where they belong. Easy!
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Good tip, but I would like to offer one simplification. Finding the contour at 0 is unnecessary. After selecting the objects and entering the MOVE command, simply select the displacement option enter 0,0,86 or whatever elevation your contours are off.