Steps to Reproduce:
1. Create a new world in 1.20.5 pre-release 1 (may also be a bug in previous snapshots)
2. Locate a trial chambers structure
3. Locate the Eruption chamber
4. Open the dispenser inside the fountain on the center platform.
5. Examine if there is a water bucket inside or not.

The file attached shows the dispenser which should contain a water bucket.
I did not tamper with the dispenser before opening it and taking this picture.