Duplicate Timeline causes rainbow color wheel cursor

I am presently running DRS 16 Beta 3

In the media page, whenever I duplicate a timeline, it generates a black thumbnail. The moment I click on the duplicated timeline, the mouse cursor turns to the rotating rainbow color wheel for around 15-20 seconds.

After that the thumbnail appears and I am able to work on the duplicated timeline or rename it.

This problem also occurs when I switch timelines.

Never had such issues in DR 15, cant be sure of previous versions of DRS 16 Beta 1& 2 as I did not try the duplicate function in those versions.

Any suggestions to overcome this is much appreciated, else will hope for a fix in the upcoming BETA version along with the fix for the problem of DUPLICATED TIMELINES not showing the proper name in the EDIT page.

https://drive.google.com/file/d/1z9wSn708UftoR4Ljr1r6P-FnMCQHouFe/view?usp=sharing

I have found that large timelines take a while to duplicate and rebuild thumbnails.

Thanks for your input Peter.

I did doubt that, but the initial timeline was an hour long video containing Q & A session, but I had to break it down to 12 individual Q & A clips on separate timelines.

In spite of the timeline shrinking with each progressive timeline that I duplicated, it still was really very annoying to work with.

Even switching timelines is painfully slow.