Has the known BUG in P4W been fixed in new Planner, in that projects which are copied loose critical data such as task assignments and task durations? This has been a known issue for three and a half (3 1/2) years. MS blithely admitted your task assignment will be tossed in the bin when you copy a project in P4W.
. It happens even if you import a .mpp from MS-Project into P4W.
"Copying a project does not copy over task assignments or the connected O365 group. However, you can always re-assign the project to the same group (or a different one!)."
Reassign hundreds of tasks and re-create durations because MS didn't think the PM's data was important enough to retain . . . really? 
https://techcommunity.microsoft.com/t5/project-blog/copying-projects-in-project-for-the-web/ba-p/1477766
I sure hope the new planner is going to be a great improvement over P4W. But judging from the experience of the "New" Teams, not holding my breath -- I will will check out Monday.com which has been referenced several times.