Due to the recent changes in the trial chambers structure, when creating a new world and loading it up, this content log error appears:
[Structure][error]-[[Jigsaw Structure]] Empty or non-existent pool: 'minecraft:trial_chambers/chamber/addon/c6'

This is similar to MCPE-179139, however, this one can only happen in the world created after Preview/Beta 1.21.0.23.