Power Automate | The response is not in a JSON format.

I have created two Power Automate flows, which technically merge up to 15 PDF files into a single PDF file. This flows runs daily. Most of the flows runs are successful, but every now and then, I receive the following error message:

Code: 400

Message: "The response is not in a JSON format."

innerError: "HTTP Status 400 – Bad Request"

I checked the involved PDF files (the files that should be merged) and there appears to be no issue with those files. I can open all of them and the same is true for the account used to execute the flow.

I also checked the input used to feed the "Merge PDF" activity and I did not see an error or issues.

Based on the rror message, I would assume something went wrong in the internal communication of the "Merge PDF" activity and the Adobe Servers, but I neeed to understand, what exactly went wrong so avoid this awkward error.

Anny ideas or hints are much appreciated