Error: Call to a member function getRegion() on null in twigsuggest_theme_suggestions_block()

I'm using the module Fixed Block Content → which

provides a way of having permanent custom content blocks without broken instances if the block does not exist.

When Twig Template Suggester is enabled and I land on a page with a fixed block, I get this error:
Error: Call to a member function getRegion() on null in twigsuggest_theme_suggestions_block() (line 30 of modules/contrib/twigsuggest/twigsuggest.module).
The issue lies in the block not being loaded (NULL): $block = Block::load($variables['elements']['#id'])
Its ID comes in a different format: fixed_block_content:my__block_machine_name.

Adding a simple check sorts the issue. Patch attached.