Serious bug in 18.6.6

Working on a long time project 52min documentary, started on a previous version and working well on several updates, I am facing a serious problem on 18.6.6 version
When I duplicate the main timeline, I obtain of course a copy of it, but in both timeline, the new one and the original one, I loose color correction on some clips. I mean in Color, all the nodes are gone except an empty one. On the original timeline, if affect a minority of clip, and many more on the copy.
I try to find out looking for common point in terms of type of clip or corrections used, but can't find a logic yet. It can affect a specific clip on the copy and not on the original, a clip with a specific correction and not his nearby brother who's got the same nature and correction... I am getting mad!
With this kind of big project with hundreds of clips and corrections it's a just dramatic cause you start to doubt about any clip in the movie that may lost correction any time, while you are at the end of the work!
Don't know what to do, coming back to a previous version or jumping to 19... ??

Sorry, I corrected my previous message to be more precise : it is version 18.6.6. I was before on 18.6.5 ( and previous...) and cannot certifie the bug was not already there...

I did more test, and can reproduce easily the bug, even with a simplified version of the timeline. It is mainly ProRes Blackmagic camera files, ProRes After affects clips and H264 clips from other cam. problem happen indifferently on all formats.

Does not happen with a very new project using the same files, so it really seems to be an "old project problem"

And I install and try Version 19 : Exact same problem !!!!

Did you keep a backup as it was advised?
If so, go back to the older version and export the project from there (.drp). Now upgrade again, make a fresh Library (aka database) and import. Does it now keep the grades?