There have been reports of Autodesk apps that are using the plug-in auto loader mechanism breaking after the install of AutoCAD 2017 Service Pack 1. I know we've had at least one individual internally to our company have this issue, and it's been happening more and more.
The problem appears to only happen in vanilla AutoCAD and not in verticals like AutoCAD Architecture. A workaround is to remove the SeriesMax entry from the PackageContents.xml. For example: xmlSeriesMax="R21.0". Or to change it to xmlSeriesMax="R21.1".
You can read more about it on the JTB World Blog here: AutoCAD 2017 Service Pack 1 and a word of warning
JTB World also released an Autodesk hotfix that addresses this issue which, at the time of this publication, was not yet made public: AutoCAD 2017 App Autoloader Hotfix