When an entity is repeatedly teleported between dimensions to a chunk that is loaded, it will eventually cause the entity to stop existing until relog.
To reproduce:
1. /execute in minecraft:overworld run setworldspawn 0 0 0
2. /execute in minecraft:the_nether run tp @s 0 0 0
3. /summon minecraft:armor_stand ~ ~ ~ {NoGravity:1b,Tags:[foo]}
4. /execute in minecraft:overworld run tp @e[tag=foo] 0 0 0
5. /execute in minecraft:the_nether run tp @e[tag=foo] 0 0 0
6. Repeat previous two steps with a small delay between them until you get 'No entity was found'
7. /execute in minecraft:overworld run tp @s 0 0 0
8. You will see the armor stand for a split second before it disappears
9. /say @e[tag=foo]
10. Exit and rejoin the world to see the armor stand has returned1. /execute in minecraft:overworld run setworldspawn 0 0 0
2. /execute in minecraft:the_nether run tp @s 0 0 0
3. /summon minecraft:armor_stand ~ ~ ~ {NoGravity:1b,Tags:[foo]}
4. /execute in minecraft:overworld run tp @e[tag=foo] 0 0 0
5. /execute in minecraft:the_nether run tp @e[tag=foo] 0 0 0
6. Repeat previous two steps with a small delay between them until you get 'No entity was found'
7. /execute in minecraft:overworld run tp @s 0 0 0
8. You will see the armor stand for a split second before it disappears
9. /say @e[tag=foo]
10. Exit and rejoin the world to see the armor stand has returned
fixed in 20w45a