Using Adobe Premiere Pro CC 2017.1.2
I appreciate Trevor’s post but it didn’t work for me but it got me playing around and I hit upon what seems to work.
(I also agree with Greg that Premier is an inferior tool for the job unless/until Adobe gets their cow pies in order.)
How to fix open captions in Adobe Premier Pro that decided to drift off to another position:
Click the purple part of the box that contains all the black open caption bits inside.
Using the captions window, make sure the first caption is selected
Scroll down and shift+click the last one (in between the in and out time codes is a good spot)
With the entire series of captions in this open caption file selected, click the bottom center (or whichever one you want) filled in which may take several clicks till it registers.
With all still selected, retype the number in the font size.
Voilà the text that was pushed off to the right (or wherever) should all pop back into it’s proper place.
Granted this fix assumes all your open captions are the same size but it’s probably all most people need until the code team is locked into a room till they squash this bug in the next release (2017.1.3?).