If you activate the Default Connected Textures texture pack while using Sodium, Sodium's custom biome blend breaks and the game instead uses the default vanilla one. I don't know if this is an issue on your side, if it isn't, I'll report it to the Sodium devs as well.

Mods used:

• continuity-3.0.0-beta.4+1.20.2
• fabric-api-0.96.3+1.20.4
• indium-1.0.30+mc1.20.4
• sodium-fabric-0.5.8+mc1.20.4

Vanilla/Broken Sodium biome blend:

Custom Sodium biome blend:

It's an Indium issue. It may not be worth reporting as Sodium will soon include a native FRAPI implementation that does not have the issue.

Thank you for the quick answer, I've heard about Sodium's future FRAPI implementation and as it is just a small issue, I won't be reporting it to them.