so I'm using the appimage version 19.11.80, but I've tried every other version after 17 and they all do the same.
If your clip is paused, you cannot scrub to different time. If the clip is playing, then you can grab the (upside down white triangle) marker and drag to a different time, or just click and play from that point. The abherant behavior can be seen here. https://youtu.be/aLbT1EF26ns. The correct behaviour is shown here https://youtu.be/LnzkU2vD4Ho for ver 17

Instead of grabbing the current time place marker, it places some little blue rectangle on the timeline.

Toggling View->Project Monitor makes no difference.
Toggling the flag button at the bottom right of the screen makes no difference.

Does anyone have a fix for this frankly annoying behavior ?

agro.

I tested the following on Windows version: drag a clip from clip bin to the timeline. Grab the playhead and move it. 17.12 = smooth. Past 17.12 I have to wait a couple of seconds before I can move the playhead. If I move the playhead immediately after dragging the clip into the timeline I get this blue line as well.

Can you confirm this behavior of steps?
Do you work with the Windows version and with an i7 CPU?

I can confirm this problem - this make editing extremely uncomfortable.

Strangely this problem goes away (for me) when enabling movit (the buggy gpu acceleration), however then I cannot use cpu rendering anymore, doubling my rendertime. All parameters I set in render seem to be ignored from then on.

I am currently travelling with a laptop with uptodate Manjora and kdenlive 19.08.2 on a quadcore intel i7-4910 with nvidia geforce gt 730m, but I have the same problems at home with an 8-core Ryzen processor and Nvidia GTX 1050.

Basically if you enable movit, you can edit videos, but not render, if you disable movit you cannot edit but render movies.

Thanks for this input. The dev's are supposing this is a MLT problem for a long time. I heard that MLT will work on this problem.

We are trying to debug this issue. Seems to be MLT related...

https://github.com/mltframework/mlt/issues/498