Instant Run is a technology that allows you to reduce the time to build a project ( while the time of the first build is increased ).
But there is one very big BUT : using this technology, in some cases you may get incorrect behavior of your programs.
In the official documentation, Google itself writes something like: "... for the correct functioning of the name_ of something the Instant Run technology must be turned off."
If you know all those situations where using Instant Run can lead to incorrect results, then in principle, you can use it, but something tells me that using this technology may affect the behavior of your program even in some case, which It is undocumented, so I would still advise not to use it (at least for now).
More information about Instant Run can be read in this article , or in the official documentation.
UPD. How to disable Instant Run:
File - Settings - Build, Execution, Deployment - Instant Run - uncheck Enable Instant Run...