I'm having a strange issue using the pico-8 TweenMachine library created by JoebRogers. When I create multiple instances of a tween, they seem to be interfering with each other. Lets say I have a tween for the player in the player class:

pl={
 x=0,
 y=0,
 sprite=0
}
pl.tween=tween_machine:add_tween({
 func=inback,
 duration=0.45
})
pl.tween:register_step_callback(pl_update_y)
pl.tween:register_finished_callback(pl_tween_end)

That works as expected. However, when I try to update tweens created for enemy objects, the enemy movement (processed by the enemy tween) is causing the player to move erratically. When I remove the enemy tween the player tween works fine again. Here's how I create enemy objects:

enemy_group1={}
for i=1,max_group_enemies do
  enemy={
   etype=1,
   width=0,
   height=0,
   edir=⬅️,
   tween=tween_machine:add_tween({})
  }
add(enemy_group1,enemy)

Basically, each enemy has its own tween, and is updated each frame like this:

if e.state==1 then
  e.tween.v_start=135
  e.tween.v_end=-15
  e.tween.duration=4.27
  e.tween.func=linear
  e.state=2
 else
  e.x=e.tween.value
  if e.x<-8 then
   e.alive=false
   enemies_alive-=1
  end
end

The only difference between the two (player/enemy) tweens is that I use a callback for the player tween to update player position, but access the tween's value directly to update enemy positions.

I'm new to pico-8 development, so it's quite possible I'm misunderstanding something on the Lua side of things. Any insight much appreciated.