SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data

[jangrewe]

Describe the bug A clear and concise description of what the bug is.

To Reproduce Steps to reproduce the behavior:

1. Go to Spool
2. Click on "Print Labels"
3. See white page with "loading" in the top left corner, then for a split-second there's the Spoolman page layout, and then it's completely white again

Expected behavior Print label dialog/page

Screenshots < white rectangle here >

Spoolman Host (please complete the following information):

• Installation type: Docker
• Installed version: 0.20.0
• OS and Distro: -
• Database type: MySQL

Desktop (please complete the following information):

• OS: Windows
• Browser Firefox

Additional context

22:43:53.344 SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data
    <anonymous> https://spoolman.faked.org/assets/saveload-DI81B4kS.js:1
    M9 https://spoolman.faked.org/assets/index-BK6PK94R.js:39
    useState https://spoolman.faked.org/assets/index-BK6PK94R.js:10
    N https://spoolman.faked.org/assets/saveload-DI81B4kS.js:1
    Ge https://spoolman.faked.org/assets/spoolQrCodePrintingDialog-BpyB7WwO.js:1
    _E https://spoolman.faked.org/assets/index-BK6PK94R.js:39
    qM https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    VM https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    FK https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    Dg https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    f3 https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    jM https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    S https://spoolman.faked.org/assets/index-BK6PK94R.js:26
    M https://spoolman.faked.org/assets/index-BK6PK94R.js:26
    EventHandlerNonNull* https://spoolman.faked.org/assets/index-BK6PK94R.js:26
    <anonymous> https://spoolman.faked.org/assets/index-BK6PK94R.js:26
index-BK6PK94R.js:41:161

22:43:53.344 SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data
    <anonymous> https://spoolman.faked.org/assets/saveload-DI81B4kS.js:1
    M9 https://spoolman.faked.org/assets/index-BK6PK94R.js:39
    useState https://spoolman.faked.org/assets/index-BK6PK94R.js:10
    N https://spoolman.faked.org/assets/saveload-DI81B4kS.js:1
    Ge https://spoolman.faked.org/assets/spoolQrCodePrintingDialog-BpyB7WwO.js:1
    _E https://spoolman.faked.org/assets/index-BK6PK94R.js:39
    qM https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    VM https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    FK https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    Dg https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    f3 https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    jM https://spoolman.faked.org/assets/index-BK6PK94R.js:41
    S https://spoolman.faked.org/assets/index-BK6PK94R.js:26
    M https://spoolman.faked.org/assets/index-BK6PK94R.js:26
    EventHandlerNonNull* https://spoolman.faked.org/assets/index-BK6PK94R.js:26
    <anonymous> https://spoolman.faked.org/assets/index-BK6PK94R.js:26
lockdown-install.js:1:97687

Spoolman is running behind a Nginx with HTTPS and WebSockets enabled.