Just start subtitles again
Every time I use the subtitle tool I encounter a new issue, clearly this feature hasn't had much testing, with multiple forums posts showing many users experiencing the same difficulties:
Export options disappearing (solution: roll-back to an obsolete version of premiere)
Title tracks not updating in timeline despite being updated in the subtitle tool (solution: edit the set file externally)
Not being able to export baked-in captions through media encoder (apparently fixed but I still have this issue)
Free subtitle software, and even the free version of DaVinci Resolve makes subtitling far, far easier, so why not just start again Adobe?
Redesign the tool, make it easier and more reliable.

Well . . . that’s exactly what we did :)
We have completely redesigned the captioning workflow in Premiere Pro version 15.0. You will see many dramatic workflow improvements. Please update to the latest version.
Learn all about the new captions workflow here: https://helpx.adobe.com/premiere-pro/user-guide.html/premiere-pro/using/working-with-captions.ug.html