Laravel queued emails throws exception after some are sent - laravel

Question

I have an Laravel 5.4 app.
My issue is that I have a weekly job that queues some emails.
Like this:
Mail::to($user)->queue(new \App\Mail\INBND10\i01($user));
Everything looks fine, and some of the emails were delivered, but I got a Trying to get property of non-object Exception after a couple of emails are sent.
Sentry tells me that is in the Mail build method, as seen here:
Any ideas what causes this oddly behavior?
EDIT
StackTrace
ErrorException: Trying to get property of non-object
#40 vendor/laravel/framework/src/Illuminate/Mail/Mailable.php(462): handleError
#39 vendor/sentry/sentry/lib/Raven/Breadcrumbs/ErrorHandler.php(34): handleError
#38 vendor/laravel/framework/src/Illuminate/Mail/Mailable.php(462): setAddress
#37 vendor/laravel/framework/src/Illuminate/Mail/Mailable.php(346): from
#36 app/Mail/INBND10/i01.php(35): build
#35 app/Mail/INBND10/i01.php(0): call_user_func_array
#34 vendor/laravel/framework/src/Illuminate/Container/BoundMethod.php(29): Illuminate\Container\{closure}
#33 vendor/laravel/framework/src/Illuminate/Container/BoundMethod.php(87): callBoundMethod
#32 vendor/laravel/framework/src/Illuminate/Container/BoundMethod.php(31): call
#31 vendor/laravel/framework/src/Illuminate/Container/Container.php(539): call
#30 vendor/laravel/framework/src/Illuminate/Mail/Mailable.php(116): send
#29 vendor/laravel/framework/src/Illuminate/Mail/SendQueuedMailable.php(52): handle
#28 vendor/laravel/framework/src/Illuminate/Mail/SendQueuedMailable.php(0): call_user_func_array
#27 vendor/laravel/framework/src/Illuminate/Container/BoundMethod.php(29): Illuminate\Container\{closure}
#26 vendor/laravel/framework/src/Illuminate/Container/BoundMethod.php(87): callBoundMethod
#25 vendor/laravel/framework/src/Illuminate/Container/BoundMethod.php(31): call
#24 vendor/laravel/framework/src/Illuminate/Container/Container.php(539): call
#23 vendor/laravel/framework/src/Illuminate/Bus/Dispatcher.php(94): Illuminate\Bus\{closure}
#22 vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(114): Illuminate\Pipeline\{closure}
#21 vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php(102): then
#20 vendor/laravel/framework/src/Illuminate/Bus/Dispatcher.php(98): dispatchNow
#19 vendor/laravel/framework/src/Illuminate/Queue/CallQueuedHandler.php(42): call
#18 vendor/laravel/framework/src/Illuminate/Queue/Jobs/Job.php(69): fire
#17 vendor/laravel/framework/src/Illuminate/Queue/Worker.php(317): process
#16 vendor/laravel/framework/src/Illuminate/Queue/Worker.php(267): runJob
#15 vendor/laravel/framework/src/Illuminate/Queue/Worker.php(113): daemon
#14 vendor/laravel/framework/src/Illuminate/Queue/Console/WorkCommand.php(101): runWorker
#13 vendor/laravel/framework/src/Illuminate/Queue/Console/WorkCommand.php(85): fire
#12 vendor/laravel/framework/src/Illuminate/Queue/Console/WorkCommand.php(0): call_user_func_array
#11 vendor/laravel/framework/src/Illuminate/Container/BoundMethod.php(29): Illuminate\Container\{closure}
#10 vendor/laravel/framework/src/Illuminate/Container/BoundMethod.php(87): callBoundMethod
#9 vendor/laravel/framework/src/Illuminate/Container/BoundMethod.php(31): call
#8 vendor/laravel/framework/src/Illuminate/Container/Container.php(539): call
#7 vendor/laravel/framework/src/Illuminate/Console/Command.php(182): execute
#6 vendor/symfony/console/Command/Command.php(251): run
#5 vendor/laravel/framework/src/Illuminate/Console/Command.php(167): run
#4 vendor/symfony/console/Application.php(946): doRunCommand
#3 vendor/symfony/console/Application.php(248): doRun
#2 vendor/symfony/console/Application.php(148): run
#1 vendor/laravel/framework/src/Illuminate/Foundation/Console/Kernel.php(122): handle
#0 artisan(35): null

Answer 1

In case someone stumble on this.
We use Laravel Forge to deploy our app, and although I run the php artisan queue:restart command in every deploy, some of the workers were never restarting, some of them were up for more than 12 days.
So, when one of those workers were assigned to run the job they crashed, because they didn't have the updated code.
That's why some of emails were sent before it crashed.
HOW TO FIX
To fix that when I create the queue workers on Forge I had to set a timeout value. So in that way, none of the workers will get frozen, and they will be restarted as expected.
https://laravel.com/docs/5.7/queues#job-expirations-and-timeouts