See if there is anything in the Reel Name column in Resolve's Media page. If not, trynchanging the settings in Resolve to derive the reel number and export a new AAF after rendering out the clips.

It can be caused by doing any modifications to the sequence while in Resolve and not generating a new AAF. Or a corrupt clip. Basically there isn't media where media is expected.

Short asnwer, no. Frame Flex works on Master Clips. What you do with those clips will have the Frame Flex applied (or not if you wish). The purpose of Frame Flex is to allow the addition of removeable effects to clips on the timeline. The catch is that once you apply a Frame Flex setting to a clip, all instances of that clip will exhibit the effect

Did you uninstall and reinstall MC when doing the OS upgrade?

Silly question: Same user settings on the timeline display in both projects? Is Show Adapters set to All?

Try changing the plug-in selection on the AMA Link. Auto detect will probably try to use the Avid Generic plug-in. Right click on that selection and go to Link with... and select Quicktime. See if that helps.

We all make mistakes. Thanks for sharing. We all learn from each other. Your reputation remains intact.

You might have inadvertently changed the playback rate of the 48 KHz audio. Check the audio import settings and see if Sample rate conversion was checked as well as Do not convert sources with pull up or pull down. Whatever they were set to, try the opposite and see if things change.

Yes, you can put a DNxHD Op1a into Media Encoder. If it can spit it out, it can bring it in. You can also restart Media Encoder and see if it works with the original file. It sometimes gets...silly. One thing you can't do with the more recent Media Encoder releases is use a QuickTime reference movie. They took the cue from Apple regarding legacy

Select segment mode (red arrow), select clips (shift click for multiple clips) with color correction, hit delete (backspace). This will remove the effect on a clip. Unfortunately, if there's more than one effect it might not remove the effect you want to remove. Otherwise, use the Symphony option. One right click and they're all gone.