This happens consistently, every time you close and reopen Chrome, the last tab will be moved right of the tab you were on when you close Chrome. Closing and reopening the browser will move another one, and so on.
If it makes it easier with numbers, lets say you have 5 tabs open and you are on tab 2, tabs would look like this originally:
1,2,3,4,5
When you close Chrome and reopen it, suddenly it looks like this:
1,2,5,3,4
Then if you close and reopen again, it goes:
1,2,4,5,3 and so on.