The short version is that you did it in the wrong order.
First, you updated trunk with the new Stable Tag here:
https://plugins.trac.wordpress.org/changeset/993543/post-deployment-hook
Then, you actually tagged it here:
https://plugins.trac.wordpress.org/changeset/993545/post-deployment-hook
So between those commits, it updated and noticed you lacked the new directory. When it updated again later, it noticed the version had not changed and so it didn’t do a full update of the readme.txt.
Admittedly, this is somewhat timing dependent.
To avoid this in the future, don’t do two commits, just do one commit with both the update and the creation of the tagged files.
Say you have a working directory:
svn co http://plugins.svn.wordpress.org/post-deployment-hook/ post-deployment-hook
In your working directory, you make your changes to trunk. Update the version, stable tag, etc. Then, you copy trunk to a tagged version:
svn cp post-deployment-hook/trunk post-deployment-hook/tags/1.0.1
Finally, you commit the whole change all at once:
svn ci post-deployment-hook -m "Update to 1.0.1"
I’ve manually triggered the process to update your plugin so it’s fixed now, but a combined method like this will work better for you in the future.
For reference, had you done another commit, to pretty much anything, that would have triggered it again and fixed the problem as well.