esp_event_handler_instance_t not defined in V4.1 - so says my compiler

[Aussie Susan]

A few days ago I created a project using the ESP-IDF framework inside PlatformIO running in Atom. At that stage it was ESP-IDF V4.0 and I coded accordingly.
Today I saw that V4.1 was released and I upgraded the framework.
I also changed some of the code to conform to the V4.1 changes in the WiFi area so that it is a (slightly) modified version of the 'station_example_main.c' example program.
That code contains a reference to a typedef 'esp_event_handler_instance_t' which the compiler now flags as undefined. However it is exactly the same as in the sample code.
Everything else seems to compile OK (including the various 'xxx_netif_xxx' functions).
Has anyone else come across this?
Susan
(BTW I'm also posting this in the PlatformIO forum as I'm not sure if it is an ESP-IDF bug or the way that it has been implemented in PlatformIO - or if I'm doing something stupid!)

[scubachristopher]

Same for me. Trying to build https://github.com/tonyp7/esp32-wifi-manager.git.

unknown type name 'esp_event_handler_instance_t'...