Hello,
I believe it might be related to another issue :
Here : https://github.com/octfx/wiki-seo/blob/master/includes/WikiSEO.php#L267
The return value of the function is always null, even though $param seems to be fine.
This causes the return value of the entire loadPagePropsFromOutputPage() function to be null, because $result ends up empty.
The call to this function is triggered because $properties is also empty here :
https://github.com/octfx/wiki-seo/blob/master/includes/WikiSEO.php#L229
Both of these calls returning empty causes $result to be empty here :
https://github.com/octfx/wiki-seo/blob/master/includes/WikiSEO.php#L107
After, that, the process continues with an empty $this->metadata, and at the next line, here :
https://github.com/octfx/wiki-seo/blob/master/includes/Hooks/PageHooks.php
empty metadata array causes the extension to revert to the default value for the image, defined in LocalSettings.php with $wgWikiSeoDefaultImage in my case.
All my other tags are also ignored, and filled with the default value.
It looks like the metadata aren't saved to (or at least retrieved anymore from) the database, without the extension being able to be backed up by the page content.
Sorry, I can't help you more than that.
If required, I'm on MW v1.38.4
Good luck Octfx :)