Sometimes your choir needs a Bottle Rehearsal.
In television, a bottle episode is one where no new sets or major production elements are needed. Often, they are not related to the ongoing plot of the series, set in a single setting or exploring a particular standalone plot.
For ensembles, think of the main “series plot” as the development and growth the ensemble makes over the course of a concert season. A bottle episode is one where you set that “plot” aside – no new sight reading, no in-depth work on the currently challenging repertoire – and devote the rehearsal to reviewing solid repertoire. It’s good fun for the ensemble, it’s good review for the music, and it’s a good way to give brains a refresh. I like it especially when the ensemble is likely to be particularly tired; while it’s still an engaging rehearsal, it’s engaging in different and potentially less mentally taxing ways.