Dissolve transition causes black bar artifact

"Device Manager does not give rollback option"

That is not the proper way.

Update or roll back your graphics driver directly from the video card manufacturer’s site:

https://www.geforce.com/drivers

Thank you all for your prompt replies - extremely helpful.

Driver for GPU (RTX2080Ti) is up to date.  Device Manager does not give rollback option.

Impact dissolve worked perfectly and solved the problem.

Thank you again.

Might want to consider using this one:

Free Impact Dissolve from FilmImpact - PremierePro.net

As Kulpreet stated, you might want to check your video card. If your video card has been recently updated, you might need to roll the update back to a previous update. Checking that you have the latest update would be a great start. Small corruption in the frames of the video clips can also be the cause of this. We had a similar issue and then we transcoded key clips in the transition in a less compressed format like Cineform/Quicktime and this seemed to help our situation. Once again, if it works unselecting Composite in Linear, there is as least a solution. For the long term, I would definitely look into updates, codecs and media issues. Have you tried different format outputs to see if the issues hold true in all cases? 

Check if you have any updates available for the GPU drivers.

-KS