Brine28

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Make sure your pack.mcmeta file uses the correct pack_format for Minecraft 1.21.7,
Also double-check that the file is valid JSON and that there are no missing or corrupted files in your assets/ folder. Even one broken texture can cause a ‘Resource reload failed’ error.

Try setting your render distance to around 12–16 chunks.

I tested this issue in Minecraft Java Edition 1.21.7, but I was not able to reproduce it.
Typing the letter “a” in chat works normally for me, and no message gets deleted.
OS: Windows 11
Java version: 24 (build 24+36-3646)
Keyboard layout: (UK)
Let me know if more specific steps are needed to trigger the issue.

I was able to reproduce this issue in Minecraft Java Edition 1.21.7.
If a player in spectator mode spectates another player who is also in spectator mode and moving, the player locator bar begins to flicker and behave unpredictably.

Additionally, I noticed that if the spectator switches to Creative mode after spectating, the locator bar continues to stay on screen and does not disappear as expected.

This behavior seems to persist even after the spectating ends.