Sorry, my English is not very good.
I have encountered this situation, usually from other programs to switch back to interactive render, it will start to work again, and I did not change the material or the scene, this restart is redundant.
There is no situation in the other renderer.
I use the system is WIN10.
3ds Max to minimize the window, and then open the program, interactive render to re work, and this new rendering is not necessary.
I think that when you change the material or edit the grid, the interactive render window will refresh, and other situations usually do not need to refresh the interactive render window.
This problem was fixed some dailies ago. Which version do you use?
1.6 daily builds
Which one?
I’m switching apps all the time and I know about this bug and I know that it was fixed 
I gues it was this build https://forum.corona-renderer.com/index.php/topic,13400.msg96209.html#msg96209
try the latest daily build, there were some fixes aimed at the spuriously restarting IR
In 1.6 RC1 did not fix, I try to minimize the 3DS MAX, and then open, IR will refresh, during which I did not change the material and the scene.
Closing and opening material editor also causes IR refresh, and I don’t have edit material.
RC5 version is not fixed, IR response is too sensitive, I just click on the map IR will restart. Can you refer to Fstorm?
are you rendering from a physical camera? If yes, does it happen also when rendering from free view? Do you have material editor open? Slate?
no response, closing down. We fixed the restarts when navigating in slate though