Before trying to debug anything, I would remove all those scripts and plugins (IMHO that's way too much plugins
, especially when you know that a lot of them are badly written and/or do not work anymore and left GIMP in an unstable state or do not reset the tools how they were before running the plugin)
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Once you've removed them ALL, (tell your friend to save them somewhere else if he really like them), try again to rotate the selection with a neat and clean installation, if it works then you know that the problem comes from the plugins > then add your plugins by group and try to rotate the selection between adding group of plugins.
(closing that webcam and other software as well before running GIMP, would be a good move to be sure nothing is interfering with GIMP)