Reposting here from the modpack tracker: EnigmaticaModpacks/Enigmatica6#4078

Not reproducible for me. Could maybe be a mod conflict.

I got a way to reproduce. Tested on 2 seperate worlds worked twice.

Minecraft 1.16.5 with Travel Anchors 2.4 + Lib X
Steps:

1. Superflat world preset "minecraft:bedrock,230*minecraft:stone;minecraft:plains"
2. /tp 1000 250 100 (probably works anywhere)
3. Place and name Travel Anchor (somewhere in the middle of the chunk?)
4. Go to adjacent chunk border (outside of chunk the Anchor is in)
5. /fill ~ ~ ~ ~ ~-100 ~ minecraft:air
6. Go to bottom
7. Place block above any vertical chunk border (blue horizontal lines in F3+G)
8. Pass below and above boarder
9. Notice while below boarder no label and while above label appears

I would like to highlight that in my E6E world some Travel Anchor labels disappear from Anchors above and below me.
This reproduces only the above case.

I have been trying to reproduce this issue, as it's sooo annoying.

I have come across it in a clean 1.16.5 instance with Travel Anchors 2.4 and Lib X. So a mod conflict is not exclusively the issue.

It happened in a superflat test world filled with stone (y=230). Could not reproduce it reliably.
I tested it with a 100 blocks deep 1 block hole at the next over chunk border.
Things to note:
-Happens only with one Anchor and Travel Staff
-It only happened below the Anchor placed at the top
-View to the sky has to be blocked by at least 1 block for the bug to occur
-The bug appears when crossing the next vertical chunk border (blue horizontal lines in F3+G) below the block blocking the sky

My testing in E6E:

There seems to be a corelation to how many blocks are in the way.
I placed a Travel Anchor inside of a mountain and one outside of it. The bug occurs at a specific chunk border, if I remove some blocks in the, the bug is gone and if I undo the change it reappears.
I could not to get it to happen again.
There was no vertical change in my position.

I have also got it to happen when flying out of and into a deep hole around y 94 with only Anchors above my y level not disappearing (no blocks blocking sky view).