This is a problem currently occurring on the dHealth project.
https://staking-explorer.com/staking/dhealth
The conditions and algorithms for becoming a Treasury wallet are unknown, but there is a bug where some Stakers wallets are automatically assigned to Treasury wallets for a while and staking rewards are not distributed. The number of DHPs held does not seem to have much of an effect.
*I am not familiar with writing about problems, so I would appreciate it if you could specify any other information you need.