This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 112e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.
According to 18.104.22.168.1 [dcl.spec.auto.general] paragraph 15,
A function declared with a return type that uses a placeholder type shall not be a coroutine (9.5.4 [dcl.fct.def.coroutine]).
This should also apply to coroutine lambdas.
Rationale (July, 2020):
No change is needed. The restriction applies to functions, and the lambda's operator() is a function.