I faced similar issues with GH4; jarring motion / judder when panned at 25p.
Test A: The situation seemed to get better (for good) - i meant lesser judder at 50p (of coarse the shutter speed had to be increase - Ts <= 1/00s) but the problem still remained.
Test B: The next step was to enable the variable frame rate to 75fps and consequently I also set the shutter speed to 1/320 s (~ 1/4 times the frame length) and panned it slowly enough to reduce the judder and it did reduce the judder. Well, in the final edit I increased the speed to 200% of the original footage to get something decent (subjective).
Conclusion: By the way, while test A produced a unacceptable video but contained the background audio; Test B produced an acceptable video with no audio (something that is stated to be common when VFR is ON).
I believe this video judder is either a
mechanical problem: Owing to the use of (slow) rolling shutter
OR
codec issue and I can't comprehend this.
By the way EOS 7d with similar settings i.e.(Full HD 25p) produced no judder when panned at the same angular velocity!
My work around:
USE GH4 sparingly for tilt / pan. For a linear slide application it might still be useful as the frame traversed is not going to get amplified with distance as is with a pan, keeping the velocity invariant with respect to the distance.
USE EOS 7D with glee:)
Overall, I am still discovering the drawbacks of GH4 although I see some definitive advantages with it...Time for a serious upgrade by Panasonic / bug fix...