Meta Box

I made a screen cast, poor quality though... sorry...

Made a test view
added post title in h2 tag
Saved it as - Custom

Oxygen template for single post - custom post type: long-stay

1. Adding the shortcode to the template throws an error 500.
2. Saving the template throws an error 500
3. Viewing the post after saving the template just shows a blank (white) page, nothing.
4. deleting the shortcode from template and saved it again
5. Viewing the post - the template is working again and render the post normally.

Sites: testsite.playagolf.se and staging.dev.playagolf.se

Screencast
https://vimeo.com/423144913/3ab0dbb00c

I use custom permalinks through Permalink Manager Pro and another custom plugin to rewrite archive Permalinks, could that be the problem?

Same error repeated on 2 different wp installs, both hosted with gridpane on Vultr HF VPS.
CPU: 2 vCore / RAM: 4096 MB / Storage: 128 GB NVMe

Thanks for looking into it...
// John