Missing (video) Asset bug - AE to Media Encoder

Is it just me? (don't seem to see anyone else reporting this online)

I've started getting a fairly disruptive error when sending projects to be rendered, from After Effects to Media Encoder. Software is up to date, Hardware is only a couple of years old.

There's a mustard coloured 'warning' label in the Title line entry on Media Encoder. On hovering over it, it mentions missing video media (MXFs). These are the videos that I'm using in the project, saved locally, in the same folder as the project. I have not changed my working practises or workflow arrangements for the last few years. This started happening a few weeks back. I've now started rendering directly from AE, lossless, to a watch folder that Media Encoder then detects after completion and rerenders into the required format for my organisation. This is obviously not optimal, and fairly annoying.

Anyone else encountering this and/or have actual, verified solutions?

Thanks in advance