html - PHP form email submission not working every time

EDIT: This is different from the possible duplicate, as
they never got the email. Mine sends randomly.

The code below has been working fine for almost
a year. For about the past week, however, it only sends when it wants to. My guys use it
at multiple locations on multiple devices, and the same thing is happeneing.

There's an html form that submits to this php
code, which then emails me and displays an html confirmation page. They're getting the
confirmation page, but I'm not getting the email. Later in the day, if I hit back, then
submit again, I do get the email.

I can't
figure it out. Any suggestions as to what's happening? I'm considering making a SQL
database that it submits to first, so that I can look up what they entered incase I
don't get the email.

Thanks!

if(isset($_POST['submit']))
            {
$to = "email_removed@gmail.com";
$subject = "Daily Inventory
            Submission";

// data the visitor provided
$location_field
            = filter_var($_POST['location'], FILTER_SANITIZE_STRING);
$yourname_field =
            filter_var($_POST['yourname'], FILTER_SANITIZE_STRING);
$biscuitsfull_field =
            filter_var($_POST['biscuits_full'],
            FILTER_SANITIZE_STRING);
$biscuitspartial_field =
            filter_var($_POST['biscuits_partial'],
            FILTER_SANITIZE_STRING);

$biscuitsemergency_field =
            filter_var($_POST['biscuits_emergency'],
            FILTER_SANITIZE_STRING);
$gravyfull_field = filter_var($_POST['gravy_full'],
            FILTER_SANITIZE_STRING);
$gravypartial_field =
            filter_var($_POST['gravy_partial'], FILTER_SANITIZE_STRING);
$eggsfull_field =
            filter_var($_POST['eggs_fullflats'],
            FILTER_SANITIZE_STRING);
$eggspartial_field =
            filter_var($_POST['eggs_partial'], FILTER_SANITIZE_STRING);
$cheese_field =
            filter_var($_POST['cheese'], FILTER_SANITIZE_STRING);
$sausagefull_field =
            filter_var($_POST['sausage_full'],
            FILTER_SANITIZE_STRING);
$sausagepartial_field =
            filter_var($_POST['sausage_partial'],
            FILTER_SANITIZE_STRING);
$jalapenos_field = filter_var($_POST['jalapenos'],
            FILTER_SANITIZE_STRING);
$sprayoil_field =
            filter_var($_POST['spray_oil_cans'],
            FILTER_SANITIZE_STRING);

$pouroil_field =
            filter_var($_POST['pour_oil'], FILTER_SANITIZE_STRING);
$tofu_field =
            filter_var($_POST['tofu'], FILTER_SANITIZE_STRING);
$almondmilk_field =
            filter_var($_POST['almond_milk'], FILTER_SANITIZE_STRING);
$veganbutter_field
            = filter_var($_POST['vegan_butter'],
            FILTER_SANITIZE_STRING);
$realbutter_field = filter_var($_POST['real_butter'],
            FILTER_SANITIZE_STRING);
$bacon_field = filter_var($_POST['bacon'],
            FILTER_SANITIZE_STRING);
$togo_field = filter_var($_POST['to_go'],
            FILTER_SANITIZE_STRING);
$hereboats_field = filter_var($_POST['here_boats'],
            FILTER_SANITIZE_STRING);
$flour_field = filter_var($_POST['flour'],
            FILTER_SANITIZE_STRING);
$potatoes_field = filter_var($_POST['potatoes'],
            FILTER_SANITIZE_STRING);

$waters_field =
            filter_var($_POST['waters'], FILTER_SANITIZE_STRING);
$oj_field =
            filter_var($_POST['orange_juice'], FILTER_SANITIZE_STRING);
$topo_field =
            filter_var($_POST['topo'], FILTER_SANITIZE_STRING);
$cokes_field =
            filter_var($_POST['cokes'], FILTER_SANITIZE_STRING);
$comment =
            filter_var($_POST['comment'],
            FILTER_SANITIZE_STRING);




//constructing
            the message

$body = " 
Location: $location_field\n
            
Employee: $yourname_field\n\n 

Biscuits_FULL:
            $biscuitsfull_field\n
Biscuits_Partial:
            $biscuitspartial_field\n
Biscuits_Emergency:
            $biscuitsemergency_field\n\n

Gravy_Full:
            $gravyfull_field\n
Gravy_Partial:
            $gravypartial_field\n\n


Eggs_Full:
            $eggsfull_field\n
Eggs_Partial:
            $eggspartial_field\n\n

Cheese:
            $cheese_field\n\n

Sausage_Full:
            $sausagefull_field\n
Sausage_Partial:
            $sausagepartial_field\n\n

Jalapenos:
            $jalapenos_field\n\n


Spray Oil Cans:
            $sprayoil_field\n
Pour Oil : $pouroil_field\n\n

Tofu:
            $tofu_field\n
Almond Milk: $almondmilk_field\n
Vegan Butter:
            $veganbutter_field\n\n

Real Butter:
            $realbutter_field\n\n


Bacon:
            $bacon_field\n\n

To Go Boxes: $togo_field\n
Here Boats:
            $hereboats_field\n\n

Flour: $flour_field\n
Potatoes:
            $potatoes_field\n\n

Waters: $waters_field\n
Daiya:
            $oj_field\n

Topos: $topo_field\n
Cokes:
            $cokes_field\n\n






Message:\n\n
            $comment";


mail($to, $subject,
            $body);

// redirect to confirmation
header('Location:
            confirmation.htm');
} else {
echo "Error, not
            sent";}
?>