I really can't tell what the problem is.

The problem is you gave fake data for your problem instead of real data.

fake data => fake solution

(not to mention wasting time).

#!/usr/bin/perl -l

# http://perlmonks.org/?node_id=1177217

use strict;
use warnings;

my @ar1=qw(F40_I_VBBG_RI50-FMVSS301n-2SR424M-HCH-D_01EK101.a3db    
           F40_I_VBBG_RI50-FMVSS301n-2SR424M-HCH-D_01EK101a.a3db 
           F40_I_VBBG_LR50-ECR17p-2SR424M-HCH-D_01EK101g.a3db 
           F40_I_VBBG_LR50-ECR17p-2SR424M-HCH-D_01EK101k.a3db 
           F40_I_VBBG_LR50-ECR17p-2SR424M-HCH-D_01EK101.a3db );

print for values %{{ map { /(.*\d)[a-z]?\./, $_ } sort @ar1 }};
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