When in Creative Mode, the inventory GUI does not return to the center of the screen once a potion effect has expired.
Steps to Reproduce:
1. Go in Creative mode.
2. Give yourself a potion effect. (/effect give @s minecraft:regeneration 5 1)
3. Open up your inventory and wait for the potion effect to expire.
4. You will notice the Inventory GUI does not return to the center of the screen.
After the potion effect has expired, the inventory GUI is left towards the right side of the screen.
The Inventory GUI should return to the center of the screen once the potion effect has expired.
I've attached two images. In one of them you can see me with a potion effect whilst the Creative Inventory GUI is open. When the potion effects expire you can see that in the other image, the inventory GUI does not return to the center of the screen.
This works with any potion effect at any amplification.