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With the upgrade to python3, some of the python modules were upgraded to newer versions that can cause a few issues. For example, python-swiftclient caused a duplicate Content-Length header to be inserted and unicodecsv expected a bytestream instead of unicode. These issues are fixed as and when they are discovered.
Themes upgrade
If you are using custom themeing for your instance, check if any stying changes made for juniper are needed and update your custom theme accordingly.