I believe there is a bug with Annotation in Beta 6
Can you reproduce this:
1 - Select a PDF document
2 - Open the Editing Bar and select the Rectangle annotation tool
3 - Place a rectangle annotation in the document. In the Annotation Inspector, add some text in the details fiel
On my system, these steps repeatably freeze the document preview pane - it does not change if I select other documents. I can only fix it if I exit DT3 and restart.
Not seeing an issue here. Does it persist after a machine reboot?
The reboot fixed it - thanks
And I see that you have added the feature to highlight in the annotation inspector pane the selected annotation - very nice.
One other question/observation:
Whenever I add a new annotation I get this popup box - is there a way to suppress that?
No. That is is Annotation Properties pane, which was also present in DEVONthink 2.
It seems to me that if I want to make a bunch of similar annotations on a document it would be helpful to configure the annotation once and not have to close the window every time I make a new annotation.
Surely others must experience this too?
I have actually never heard any complaints in the last 7+ years 
If this should happen again, then please launch Apple’s Activity Monitor application (see Applications > Utilities), choose the frozen DEVONthink 3 in the list of processes, select the menu item View > Sample Process and send the result to cgrunenberg - at - devon-technologies.com - thanks in advance!