MD after running about 2000 steps, electronic steps cost more time,even longer than 1000s

[jumin... at gmail.com]

Dear  cp2k users and developers,
         I run MD at NVT, however, after run about 2000 steps, the job run 
slowly and slowly. if I restart the job from the slow step point, the job 
can run fast like at start time.  anyone have the similar problem?
         I attach my input. 


 mixed_precision    : F

  ----------------------------------- OT 
---------------------------------------

  Step     Update method      Time    Convergence         Total energy   
 Change
  
------------------------------------------------------------------------------
     1 OT DIIS     0.15E+00   94.8     0.00003762     -1903.1123236014 
-1.90E+03
     2 OT DIIS     0.15E+00 1387.5     0.00002286     -1903.1127142782 
-3.91E-04
     3 OT DIIS     0.15E+00  143.4     0.00001048     -1903.1129615906 
-2.47E-04
     4 OT DIIS     0.15E+00  264.3     0.00000683     -1903.1130262224 
-6.46E-05

  *** SCF run converged in     4 steps ***


  Electronic density on regular grids:      -1312.0000002470       
-0.0000002470
  Core density on regular grids:             1311.9999997705       
-0.0000002295
  Total charge density on r-space grids:       -0.0000004765
  Total charge density g-space grids:          -0.0000004765
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