Please follow step by step
1. Use your database backup copy which you made before this plugin update. Messages once updated cannot be updated again. So make sure you are using backup copy of your database which backup you made before this plugin update to 10.1.1.
2. You can use github verion OR you can use current PRO version. If you use PRO version make sure to make these 2 changes https://github.com/shamim2883/front-end-pm/commit/2d0eec44b5824bd5526d0b9532d309771700a533 and https://github.com/shamim2883/front-end-pm/commit/ec6221f36e4d451140683380da9d1e547605c940
3. Now click “Proceed” in admin notice and continue update.