Issues syncing mpp and sharepoint

[saurabhk9]

I have a Microsoft project 2016 file. I sync this file back to a SharePoint list. To begin my daily process, I always begin by going to my SharePoint list in browser(internet explorer), and click on "Open with project". This opens the sharepoint list in my local copy of Project. I then make any required bulk edits in my mpp, and save it. This triggers a sync back to SharePoint. 

It works correctly a number of times, but sometimes when I hit save in my mpp, get error : 

Sorry, we couldn’t sync the tasks list to the SharePoint site. Please make sure that: 
The SharePoint site is running and is not in read-only mode 
you have sufficient privileges to sync to this SharePoint site 
The tasks list is still available and its name hasn't changed 

None of the above apply to me, and I am not sure why sometimes my mpp just fails to sync. This is specially a big frustration, when I just finishing spending an hour with lots of changes, and then mpp fails to sync and I have to throw away all the edits. I also think this error is coming up more and more frequencty over the weeks.

Till date, I have tried a lot of possible solutions, but non worked. I tried opening from different browser, clearing my cache, opening the mpp directly from site assets, checking the file out to me etc. Please help as this is affecting the productivity of our org. 

[#2]

@saurabhk9 Try to check out and check in that file.

[#3]

@shobhitbhalla Thanks for replying.

I checked out just now, checked it in. Then tried to open the mpp and still got same error. Then I checked the file out, opened the mpp but still got the same error, so later checked in the file.

This is really worrying me now as I am running out of ideas.

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[#4]

@saurabhk9 

I had similar issues with MS Project repeatedly not synching some tasks, including some ghost tasks in the SharePoint list where I had moved tasks from the top of the MS Project plan to the bottom.  Solved by deleting the tasks in the SharePoint list (all of them), which was quite quickly done by deleting the parent tasks to delete all their children.  I then had an empty list on SharePoint.  I returned to MS Project and saved the plan to synch it back to SharePoint.  I accepted the warning message that SharePoint was undeleting list items and the end product was a SharePoint list with list items that correctly reflected the content of the MS Project file.  MS Project and the list are now synching correctly.