Hi,
In activity diagrams I frequently need flows like this:

None of the currently documented plantUml loops (repeat, while) support this. As one possible workaround I implent the same logic like below, needing to unnecessarily repeat at least one activity:

I suppose that the semantics of repeat or while cannot be changed, because it would break existing diagram specifications. What about adding a new loop type like that (wording can be improved):
start
loop
:try something;
loop if (done?) is (false)
:wait;
endloop
stop
This would make some diagrams more compact and improve readability by avoiding repetition of identical activities.
What do you think?
Best regards,
Jakob