Using 4.10
Starting with a long, single clip (e.g. 6 hr), add it to the sequence, and pan thru it on the timeline. When I find a section that I want to include in the final product, I copy/paste the clip so I now have two copies. I drag the clip boundaries to the time that I want included, then repeat for multiple clips (e.g. 50). Then I play back the video using the main arrow under the Sequence Preview window. So far, so good.
The problem occurs at some of the clip boundaries: the audio plays back unimpeded, but the video stalls with a "building preview" message. I can understand it happening once per transition, but it occurs multiple times when I play back thru the same transition. This can occur on several of the transitions, but not all of them. And not in sequence - some of the earlier transitions stall, while the later ones play back properly.
Further, sometimes a transition plays properly one time, but then falters when I play through it a second time. No recognizable pattern to how it reacts.
I've tried "scrubbing" thru the clips when zoomed in tightly, and scrubbing thru the Sequence. Sometimes it helps, other times it makes no difference. I've "clear cache of all unused clips", but it did not make a difference. There is lots of available space on the drive, and the maximum cache size is set to 100000 MB in Tools > Options > Disk. The cache is currently about 7.5 GB for the current project with one source file. The cache had previously been about 18 GB for another similar sized project, and about 28 GB when two projects were cached. It never grew beyond about 28 GB, even after starting a third project.
Is there some technique to ensure smooth preview playback?