Hi I think I solved this issue. In my case I solved this with nginx configured with ssl, as per the installation instructions. At first, I was guessing I could skip ssl, so I commented out the ssl part of the processmining.conf file. Moreover I was also starting by accessing process mining directly from the 8080 jetty embedded port, just for the sake of trying out without nginx.
Since I (1) configured ssl on nginx and (2) started accessing process mining from nginx (not the embedded jetty) everything started to work fine.
Hope this may help should anyone get into the same path as I did.
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