I have found that if you summon an a small Armor Stand, it will become invisible. I don't think this is a duplicate of "Entities become invisible under certain conditions", because the problem shows itself the second you summon the Armor Stand.
Steps To Reproduce
1. Make a new world (I used a superflat world with the air biome)
2. Find a place to summon Your Armor Stand (Can be on top of any solid block in the world)
3. Summon the Armor Stand using the command "/summon ArmorStand ~ ~ ~ {Small:1}
4. Observe
Thanks for reading 🙂
Cannot reproduce.