Nametags are rendered for players behind walls when the scoreboard team's nametagVisibility is set to never.

This causes problems for us because our server is a roleplay and nametags expose your identity straight away. We've had to ban this mod for now but we'd really like to allow it again as it part of the widely used Fabulously Optimized modpack.

I'll look into it, nametags have become really tricky to do right in 1.21.9+.

Can you provide an example on how to spawn an entity that replicates that behavior? Like how the team/subtitle is set up?

Is this on minecraft 1.21.10 or an older version?

Yeah on the latest versions of the mod and on 1.21.9/1.21.10. Started a few days ago with the latest release

Fixed in 1.9.1 but players reporting this seem to have 1.9.0 due to a modpack.