When using a repeating command block to teleport an entity with elytra to a relative location to the command block (Using ~) the entity will sometimes keep slowly gliding away from the location.
How to recreate:
Run /teleport command in a repeating command block to teleport an entity with elytra to a location relative to the command block (For example: /teleport @e[type=ArmorStand] ~ ~5 ~)