For same particle ID , particle type changed

Respected developers,
I am working on is Ni3Fe system, where Fe is type 1 and Ni is type 2.
In dump files, I found that for the same ID (Id No: 1779), particle type changed.

I carried out minimization and NPT MD at 1K, with swap moves.

Following is the dump file output for relevant particles.

Initial configuration :

ID Type Px Py Pz
1777 1 15.2788 15.2788 15.2788
1778 2 16.4407 16.4407 15.2788
1779 2 17.7118 17.7118 15.2788
1780 2 15.2788 17.0763 17.0763
1781 2 17.0763 15.2788 17.0763

After some steps:
ID Type Px Py Pz

1777 1 14.5725 14.5848 15.7675
1778 2 16.2649 16.1779 15.7855
1779 1 17.7884 17.8812 15.8092
1780 2 14.7823 17.0845 17.4316
1781 2 17.1228 14.7864 17.4929

I have used the following command for creating dump files.
dump 2 all custom 2000 dump_i110.dat id type x y z
dump_modify 2 format line " %6d %6d %12.6g %12.6g %12.6g "
dump_modify 2 sort id

What went wrong? This is the first time I am noticing this issue.
Please help me out.

It’s impossible to say without seeing your full input script(s).