I put pretty much everything that's going on in the question.
I use the DI Output for the PC Monitor and the HDMI output for my TV to play and watch stuff on. This worked like a charm since i started to use this setup. With the latest Updates for Windows and the Radeon Drivers I suddenly experienced the delay in the video signal to my TV. I don't use the sound signal over HDMI which would cure the problem but I want to use my sound system, that is connected to the soundcard which was no problem so far.
There were no hardware changes whatsoever. There was no firmware update on the LG TV.
Thanks for your help.