Are you playing on snapshot 20w22a? If so, then its a snapshot bug that lots of people encountered, but noone seems to connect this bug to snapshot version actually. Mojang probably messed newly added/changed structures item pools, beacouse when i encountered a desert temple the chests were ok. Newly generated chunks when i downgrated and optimised world to version 20w21a, were absolutely fine. Chests contained loot. Sadly old ones didnt which ispretty easy to understand why, becouse they were already opened and as you know (or not) chest loot ia generated upon opening.
I suggest you to downgrade to version 20w21a, by launching it and then optimising your world so you wont have any bugs, issues related to world corruption.
Happy to help