MTS files, Winows 10, and PP CC 2018

It's been hashed over here before, but I found a new twist. Bear with me here.

Until recently, I was running PP 2017 under Windows 7. This was because CC 2018 under Win 7 couldn't handle the MTS files I used in the project-- you know the story, the Dolby codec issue. Couldn't hear sound, couldn't see video. So, I stuck with Win 7 and CC 2017 to finish that project.

Anyway, that project's done, so I upgraded to Windows 10 and installed PP 2018. That combo is supposed to fix this problem. I opened up that old project, just to test things out... and yep, the MTS files were still marked as "Media Missing."

Now, here's the strange part. If I Import those same MTS files into a new project, most of them import without a problem. But, if I try to Replace Footage with them, to fix my old project, they won't work at all. (I also tried importing the files, and then I imported a sequence that contained those files-- but nope, the imported sequence still reported errors.)

At least Media Encoder 2018 is able to convert the MTS files to MP4, and I can use those to Replace Footage. But this means that I can't really use my old GH2 camera on projects without adding this small headache. And now I'm hoping that I can still use Encore from 2016 to make Blu-Rays and DVDs.

Advice?