This has actually occurred for several engine versions - almost as far back as 4.17. I’m not sure how it’s gone unnoticed for so long but it still occurs in 4.19.
Steps To Reproduce
Open a 4.19 project. Now open the solution file of a different project that uses the same engine version, and try to build it in visual studio. Instead of building normally, the project will try to build for Hot Reload because it thinks the project is open - but it isn’t.
This has only started happening in recent engine versions - you used to be able to have two projects open side-by-side and the hot reloader would only kick off if the same project was already open.