You're going to have to volunteer more information about software versions, computer, where the clips came from, what the clips are and how you are processing them. Nobody can guess based on the limited information you provided.
I'm using Premiere Elements 12, working on a PC, clips are my own work, AVCHD 1920x1080, 23.97 frame rate, same lighting and opacity from clip to clip. I'm out-putting as .mp4 at 1920x1080,data rate 35305kpbs, total rate 35479kbps, frame rate 24.
Please let me know if I've missed any info.
For a first guess, can you try pushing the "Advanced" button in the share section and change the frame rate to 29.97?
Changed the frame rate in "advanced" for the out put - but it's still there.
Let us go through the workflow to try to identify factor(s) that might be contributing to these flashes between video clips.
Premiere Elements 12, presumed on Windows 7, 8, or 8.1 64 bit. Have you updated 12 to 12.1 Update using an opened project's Help Menu/Update? If not, please do so.
1. Given 1920 x 1080 @ 23.97 progressive frames per second...you say you have AVCHD video compression (by the way, what is the file extension - .mts or .mp4 or something else)?
2. Are you (manually) or the project (automatically) setting the project preset? Start a new project and set the project preset manually to the following according to the details at the bottom of the following link
The project preset should be
Then in the Premiere Elements 12/12.1 Expert workspace, import your source video from its hard drive save location using Premiere Elements' Add Media/Files and Folders. Is there an orange line over that Timeline content? There should not be. With no colored line above the Timeline content or a green line above that content, is the play back flaw gone in the Edit area monitor?
If not, right click the Edit area monitor, select Playback Quality, and select Highest instead of Automatic. Are you adding effects to the Timeline content? If so, is the problem gone when no effects are added to the Timeline content?
Where are at this point of the troubleshooting...at a solution or no solution yet?
We will be watching for your results and then decide what next based on your details.
Add On...I have assumed a NTSC setup. If other please let me know.