Starting from version 1.12.2-1.8.198 the ender tether doesn't render correctly; if it's placed against a wall it becomes invisible, while if it ìs placed on the ground it appears as a missing texture block.

Tested on Forge version 14.23.2.2613 and no other mods beside Bookshelf.

Thanks, could you get a closer screenshot of the text on the block?

Thanks to you! Here you go.

P.S.: The previous screen was mainly to show the bounding box of an ender thether.

Thanks for the new picture. I will look into getting this fixed.

This issue should now be fixed in the latest version. Thanks again for the report.