The bug:

Interpolation animation of Display entities is non-deterministic for map and pack creators. That is, creators cannot guarantee that players will see the animation they want players to see. For example,

• Players who enter a server at different times may see different animations
• Players who move back and forth (which makes chunks unloaded and loaded) may see weird animations
• Players who exit and re-enter the level may see wrong animations

How to reproduce:

For convenience, I'll give a way that can be reproduced in the single-player world:

• Summon a small Text Display with nbt:

  • /execute summon text_display run data merge entity @s {text:'"test"',billboard:"center"}
    

• Change the size and start interpolation:

  • /data merge entity @e[type=minecraft:text_display,limit=1] {background:4294901760L,transformation:{scale:[10.0,10.0,10.0]},start_interpolation:0,interpolation_duration:1000}
    

• Notice the text is scaling. When scaling, exit the world and re-enter it.
• Notice the animation will jump to the end without continuing mid-interpolation.

Analyse:

The "previous" data of the entity is saved only on the client, which means that the server has no control over the data. This is a nightmare for content creators, as they have absolutely no guarantee that players will see the correct animation.