The following pairs of translation strings both are translated the same in en_US, but show up separately in the subtitles.

• "Shulker closes"
  • subtitles.block.shulker_box.close
  • subtitles.entity.shulker.close
• "Shulker opens"
  • subtitles.block.shulker_box.open
  • subtitles.entity.shulker.open

To reproduce

1. Enable subtitles
2. Summon a shulker and place a shulker box next to it
3. Open the shulker box shortly after the shulker opens
   → Two identical subtitles are displayed
4. Close the shulker box shortly after the shulker closes
   → Two identical subtitles are displayed

Video

Minecraft 1.16.5 - Singleplayer 2021-02-14 00-47-13.mp4