I've turned this into an SSCCE (as you should have done). It works perfectly.

#!/usr/bin/env perl

use strict;
use warnings;
use Image::Thumbnail;
use LWP::UserAgent;
use Test::More tests => 2;

my $file   = 'test.jpeg';
my $imgdir = '.';
my $ua     = LWP::UserAgent->new;
my $url    = 'https://www.perlmonks.org/?updated=20180808044221;node_i
+d=1000135';
my $res    = $ua->mirror ($url, $file);

ok -e $file, 'Image downloaded';
createImageMagickThumb ($file);
ok -e "thumb.$file", 'Thumbnail created';

my $query; # Used in code from 11149409 only

# Code from 11149409 follows, unaltered.

sub uploadImage {
    my  $name = shift || '';
    my  $file = $query->param('image');

    open(LOCAL, ">$imgdir/$name.jpg") or print 'error';
    my $file_handle = $query->upload('image');
    binmode LOCAL;
    while(<$file_handle>) {
    print LOCAL;
 }
    close($file_handle);
    close(LOCAL);
    createImageMagickThumb("$name.jpg");
}


sub createImageMagickThumb {

    my  $filename = shift || '';
    my $t = new Image::Thumbnail(
        size       => 100,
        create     => 1,
        module     => 'Imager',
        input      => "$imgdir/$filename",
        outputpath => "$imgdir/thumb.$filename",
    );
}
[download]

The code worked well until a few days ago. Any idea what could be wrong ?

Yes. You changed something a few days ago which broke it. Restore the machine from the backup you took a few days ago and everything will be fine.

The image file is well uploaded but no thumb created. Thanks

Well then, why not check for errors? See the Basic Debugging Checklist, https://metacpan.org/pod/Image::Thumbnail#ERRORS and How to ask better questions using Test::More and sample data.

Don't make me tap the sign...