Yes, I suspect that is what’s happening. Up until a WP Discourse version 1.7.9, none of the shortcodes in your posts would have been displayed when the full post content was published from WordPress to Discourse. The change that allowed shortcodes to be parsed before a post is published was made to deal with the new markup that is added to the raw WordPress post by the Block Editor. I may need to look at changing that.
I think that for your case it would be best to publish excerpts of your posts and use the Discourse ‘Show Full Post’ button to display the full post. It is possible to get most content from WordPress to display in expanded posts by adding selectors to the embed_whitelist_selector Site Setting. Early next week I’ll publish a topic about how to set that up.
It’s tricky to know what the issue is without being able to see the actual post content that’s being passed to Discourse. Are you able to publish posts that don’t contain the shortcode?
I can confirm that it works without the shortcode. With the shortcode in the content I am able to initally publish a post on discourse, but I cannot update it.
I set up a staging environment and can reproduce the issue
If you are interested, I can give you access via Pm