what session driver are you using? does this happen only on the live server? local working okay?

I'm using the following session driver:

'driver' => env('SESSION_DRIVER', 'file')

I have only deployed it locally with Homestead and Vagrant

i would suggest you to change the driver to database or redis and check again. i've had similar issues when using the file driver together with heavy disk activity in Laravel 5 but it seems to have fixed in 5.1 and above.

if this does not solve your problem try running xdebug to pinpoint the cause.

Redis seems to handle the image requests better but I still get logged out after a while. I'll try xdebug later today.