@arkh - Yes I think that is the problem, but the gist of the react documentation on this seems to be that the application should be responsible for cleaning this sort of thing up. (Rather than library support, I suspect.)

https://facebook.github.io/react/blog/2015/12/16/ismounted-antipattern.html

We’ll fix that on Rum side, hopefully before v16 release. @arkh is right it’s because rendering is asynchronous and we build our own queue for rendering, there might be unmounts happening before component is forced to render. This actually happens, so “just removing this check” is not an option

in fact, if you remove it you’ll just get different warning though :)

isMounted is only deprecated for user code, it’s use is completely fine inside Rum. Unfortunately you can’t tell it to React, so we’ll have to re-implement it

@tonsky OK, thanks for explaining things. Good to know.