I recently bought WPLMS and setup the theme with sample data. Few days later I upgraded the few plugins. Since them I am not able to add/create "UNITS" from front end or course create page under LMS in the left navigation bar..
Please let me know the how this issue be fixer
As you are saying that you bought wplms recently, so i guess you are using old front end edit. So please update it by using this tip:
https://wplms.io/support/knowledge-base/wplms-front-end-update/
After this try deactivating third party plugins.