2021 (18.2.1 )won't import large .mxf files

Well, if you are linking to an AE 2021 comp through Premiere 2021, one workaround is to "Render and Replace" the large .mxf with shorter clips in Premiere 2021 which allows you to use dynamic linking as expected.

If you want to directly import large .mxf files into AE 2021- apparently you can't. I least I haven't been able to. I was not able to find a workaround in AE 2021.

What I did in order to be able to link was to save my AE project as a CC 16.x file and open it in AE 2020. .mxf import and linking then worked as expected.

If your workflow is like mine, which involves roughing sequences in Premiere and then sending linked comps to AE, it gets a little more complicated if you have projects currently in the works. After saving my AE 2021 project as a CC 16.x file and then converting it to AE 2020, I deleted both AE 2021 and Premiere 2021 so I could continuing linking files with large .mxf clips.

In order to reestablish linking with my current project, I had to roll back the Premiere project from 2021 to 2021, which is not doable from inside the software. If you need to do this here's how:

https://wikis.utexas.edu/display/comm/Adobe+Premiere+Pro+CC+-+How+to+Revert+Project+Version+to+Use+in+Older+Versions+of+Premiere+Pro

So essentially, you need to go back to AE 2020 (v. 17.7) until this bug is fixed. If you're just importing directly into AE that's all you need to do. In that case you can leave AE 2021 co-installed and continue to upgrade it until the bug is quashed. Just make sure you open projects with large .mxf's with AE 2020 until it is.