A bad commit made it into the Hugo releases of versions 0.67.1 - 0.68.0
The commit was reverted in 0.68.1
It seems that the theme you are using generated its resources with one of the above versions.
To solve the issue, you need to regenerate the resources of the theme, with Hugo Extended v0.68.3 also you can notify the theme author to do the same and update the theme repo.