To find the location of the segmentation fault, you can just run lammps with the help of a debugger, e.g. gdb.
then on the gdb prompt you type:
run -in filename.in
and then wait for the segmentation fault. When it happens, you can type:
and you get a stack trace and that will indicate the location of where the segmentation fault happens.
The alternative to this is to generate a core dump:
first type: ulimit -c unlimited
then run lmp_openmpi as usual. (lmp_openmpi -in filename.in)
after it crashed, you should see a file core.###. again, you can use gdb to investigate:
gdb /path/lmp_openmpi /path/core.###
and you get a stack trace again, telling you the location (function name) of the problem.
and then you double check with the current version of lammps.