Does it work if you follow the directions below and copy the full contents of your SD card to your data drive?
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The part about your question that made me stop and do a double think for an answer related to when you wrote
This has only just started to happen
When you insert an SD card into the SD slot of a computer, typically a pop up appears asking you what you want to do
with this SD card. When things were working the way you wanted, you may have been selecting Import Photos/Videos or something else in
that computer message so that the files were copied to a location on the computer side of things. The Premiere Elements project would have
that permanent hard drive save location to reference back to. It would not have to wait for you to insert the SD card back into
the computer to get its source media from the only place it knew them to be.
Does any of that sound like it applies to your situation?
I would suggest that you transfer the files to a hard drive save location or an external hard drive and from there import them
into your project with its Get Media/Files and Folders. Lots of variations. So, we could discuss this further if we seem to be
going in the right direction.
Looking forward to your follow up.