I wanted to play on a Minecraft server Hypixel. So I logged in on lunar client in the version 1.8.9 and played for a little bit, then I decided to play on my world in the newest release 1.16.3. Upon joining 3 advancements popped up which were "cover me with diamonds", "Isn't it iron pic" and one more that I cant remember but when I went to the advancements tab by pressing "L" all of my advancements and advancement tabs were missing. I believe this was caused by switching versions.
MC-203200
Advancements lost when switching versions.
Resolved
Invalid
0
You need to use a separate game folder for 1.8.9 so the settings are stored separately.
Also, any issues caused by modified clients and servers are not supported here.