What format is your project in? UHD?

You can only delete a sequence when MC is open and the bin for that sequence is open. You can only delete a project from the project selection window or at finder Explorer level. Is this MC First or regular MC? The Avid attic will have previous copies of bins so you can always re create the project and then copy the Avid attic bins into it. But lesson

Are you linking with UME plugin and originally they linked with QT plugin? This is know to be an issue. Apparantly the old QT plugin would potenitally produce master clips 1 or 2 frames different to the new UME plugin. Clips then won't link.

Select the item you wish to export. Probably a sequence. Right click and choose Output and the expoirt to file.

Is this MC First?

The installer for First and regular MC is the same installer. It just the licensing that alters how that application launches and works.

So was the sequence the AFF from Premiere? If so that may explain it. MC will play all the tracks available in the linked master clip. But if the AFF contained source clips that indicated an audio channel that in fact was mute in the source clip then you have a problem. Sounds like the AAF is actually incorrect. It contains clips that have incorrect

I've just logged on to Avid.com and gone to the support page and tested raising a support ticket. Worked as it should. No issues raising a support ticket. I'd contact RalphC and have that looked at. Not that I've needed to use the support option often in 25 years. I feel the yearly renewal fee justified in covering the cost of the updates

http://www.nablet.com/products/plugins/avid-media-composer/arriraw-ama-plugin/

I'd suspect the projects file location. I'd create a new project in a different location / drive copy a the current bins over (so no need to rebuild) And try that. The danger is you may end up with a project unable to save changes.