A small update on this case from my side.
I opened up a support case at AVM for this issue and now we had some mails going around - but we are still at the point of exchanging support data of the AVM box with enabled and disabled acceleration settings etc.
This will take some time I think :S
@ChuckPa any ideas or more insights why this happens with plex but not (for example) with emby or when directly accessing this sites? Any chance this is related to pyhton 2.7 or some other http library of python?
