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No problem and take your time!
Do you have any idea why my (Video-)Plugins are not working?

I actually don't, but for what I know, Kodi team have done a lot of changes in plugin infrastructure, so some plugins from Leia not working in Matrix release. My current build hardly depends on Matrix changes and unfotunately can't be ported back to Leia.

Try to run them and see if there is any issues logged in kodi.log.