The bill boarding of display entities is applied before the translation, causing them to be off center.

How to reproduce
1. Run /summon minecraft:text_display ~ ~ ~ {text:'{"text":"I am off center :("}',billboard:"center"}
2. Run /data merge entity @e[type=minecraft:text_display,limit=1,sort=nearest] {transformation:{translation:[0.0f,10.0f,0.0f]}}