There might be a bug in rendering alerts.
When I preview it, it looks like the attached image.
By the way, it was rendering properly in the beta version.
I upgraded to 5.8 and updated the theme at the same time.
Yes, I have uninstalled the gfm-blockquote-admonitions plugin.
I found the problem.
The issue seems to occur when selecting a theme other than the Official Github preview theme.