Has anyone encountered such an error with Sideloadly? 

There was an issue during installation: 0: AppexBundleMissingClassOrStoryboard (Appex bundle at /var/installd/Library/Caches/com.apple.mobile.installd.staging/temp.9AR36I/extracted/Rinstagram.app/PlugIns/com.steve.commm.widgetextension.appex with id com.steve.commm.widgetextension does not define either an NSExtensionMainStoryboard or NSExtensionPrincipalClass key with a string value in the NSExtension dictionary in its Info.plist)