I copy and paste the embedded chart into a presentation, and - bingo the data is gone :-) I assume there is some problem in the creation of / data-types of the embedded data for the chart somehow.
Created attachment 65288 [details] test sheet with simple chart + data
On pc Debian x86-64, with 3.6 sources updated today (with brand new LO profile), I don't reproduce this problem. Platform specific bug ?
*** Bug 41526 has been marked as a duplicate of this bug. ***
Can't reproduce this behavior in master. @Michael: Do you still see this behavior?
As you say - seems to be fixed now in 4.0+ Thanks Markus :-)