The earliest report to our knowledge of publishers charging to re-use open access content, was by palaeontologist and renowned advocate for open access Mike Taylor who observed in 2012 that Elsevier were charging for non-commercial, educational re-use of Creative Commons Attribution licensed "open access" articles.
The journal involved was Neuron.
Below is Mike's screenshot of the amount Elsevier and RightsLink were charging to reuse a single Creative Commons Attribution licensed "open access" article:
You can read the full text of Mike's report here: https://svpow.com/2012/03/21/pay-to-download-elseviers-open-access-articles/
If you know of any earlier reports please do let us know. This is important history to document. We would like this website to be the ultimate one-stop-shop evidence dossier for the continuously-repeated failings of academic publishers.