I simplified the OP example to trap (but only sometimes!!) the bagged behaviour

#!/usr/bin/perl

use Data::Dump;
#https://www.perlmonks.org/index.pl?node_id=11132441
use strict;
use warnings;
use Tk;
use Tk::ProgressBar;

my %pid=(ex1=>{as=>'temp', val=> -21.5});

my $mw=MainWindow->new();
my $tmpbar=$mw->Frame()->pack( -padx=>30 );


my $pbar = $tmpbar->ProgressBar(
        -anchor=>'s',
        -width=>100,
        -length=>500,
        -blocks=>100,
        -gap=>1,
        -resolution=>0.5,
        -variable=>\$pid{ex1}{val}, 
        -from=>-30,
        -to=>70,
    )->pack();

my $repeat;
$repeat = $mw->repeat(500,sub{  

                                $repeat->cancel() if  $pid{ex1}{val} >
+= 65;  
                                unless ( defined $pid{ex1}{val} ){
                                    print "WARNING: \$pid{ex1}{val} NO
+T FOUND!!\n";
                                    dd %pid;
                                }
                                $pid{ex1}{val}+=5;
                                
                            });


$tmpbar->Label( -textvariable => \$pid{ex1}{val} )->pack();


MainLoop;
[download]

L*