This is present again in 1.12.1. Invisible is set and the Marker is true. The armorstand becomes dark if it's head is in the ground.
Are there any plans on fixing this?
Yeah, same problem here:
https://bugs.mojang.com/browse/MC-68496
Yeah, these tags did work in 1.7.10. Requesting reopen.
Since the attached AV1-Encoded video might not play in all browsers, here is the same Video but with the more commonly supported H264-Encoding.