Strange stress and force variations in Fe16H O-site calculations

[ieiue]

Describe the bug

I want to make cell-relax calculation of Fe16H O-site. I tried 2 options: 1. cell-relax after relax (to get the results faster); 2. only cell-relax. But it can't converge. And the change trends of TOTAL PRESSURE and LARGEST GRAD are so strange.
ERROR:

1. cell-relax after relax:
   
   

2. only cell-relax:
   
   

Expected behavior

No response

To Reproduce

Here are calculation files:

1. cell-relax after relax:
   There are 2 STRU in this files: STRU_relax for the first only relax calculation, and STRU_cell-relax is the result STRU_ION_D of the first step after converged.
   Fe16H O-site relax-cell_relax.zip
2. only cell-relax:
   Fe16H O-site cell_relax.zip

Environment

ABACUS v.3.6.0

Additional Context

No response

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[WHUweiqingzhou]

@pxlxingliang, could you have a look?

[dyzheng]

I will test it with v3.9.0