BlueMap Version:
BlueMap-1.3.0-fabric-1.16.4.jar
Server on 1.16.3

Description:

Polished Blackstone sides do not render when behind a Polished Blackstone Slab [bottom]

Unfortunately i can not reproduce this issue..

If you want me to give it another try, you can send me the region-file of your world that is including that building and your render.conf :)

You can find the region-file using bluemaps debug option in the webapp menu, then clicking on the building and it displays the region-files name -> <worldfolder>/region/<regionfile>.mca

I have requested the config and mca files from the server admin.

After a few Client Side re-render triggers it fixed itself