The bug
Some NBT tags are not kept when fish or axolotl mobs was caught water buckets.
Affected NBT tags
Invulnerable
Glowing
Health
Silent
NoGravity
NoAI
Linked issues
is duplicated by
relates to
Attachments
Comments

Can confirm in 21w03a.
Can confirm in 21w05a.
Can confirm in 21w05b.
Can confirm in 21w06a.
Can confirm in 21w07a.
Video attached.
Can confirm.