Why does a fully depreciated asset start to calculate negative depreciation?

We have a few assets that we are seeing this scenario

1. Asset was put into service in July 2016
2. Asset uses straight line deprecation, for 108 months (9 years) and a compute direction of C
3. The monthly calculated depr is 60. In the first year of depreciation the monthly amount was 30
4. In the last year of depreciation the monthly amount was 30.
5. the asset was fully depreciated in Dec 2025 (based on the 108 months it should have been fully depreciated by June 2025)
6. Then in Jan 2026 the system calculated a negative depreciation of 30.

Why would it now start calculating a negative depreciation. As of Dec 2025 it was fully depreciated and should have stopped depreciation. Can someone explain this?