1.Please check whether you project specific bundle is in active state using
http://<aem-instance>:<port>/system/console/bundles -
2. Also I think you are facing this issue with Sling model. If yes, please check the presence of that sling model using http://<aem-instance>:<port>/system/console/adapters url as shown below -
Here CompaniesModel is my Sling model -
Please confirm all these first.