How to reproduce:
1. Update Android SDK Tools to 25.3.1
- In Mac open Android Studio -> Check for updates and update Android Studio version (might be not necessary)
- In Android Studio -> Preferences -> Appearance & Behavior -> System Settings -> Android SDK -> SDK Tools
2. Create a new Unity project
3. Build and run on Android device
Result: Build fails "CommandInvokationFailure: Unable to list target platforms. Please make sure the android sdk path is correct. See the Console for more details. ..."

Reproducible: 5.5.2p2, 5.6.0b11, 2017.1.0a3

Note: I haven't been able to reproduce this issue on Windows machine. As after update via Android Studio, SDK Manager still doesn't see SDK Tools 25.3.1 version and uses 25.2.5

Workaround for the customers.

1) just open https://developer.android.com/studio/index.html
2) scroll down to the bottom of that page
3) go to downloads
4) scroll down to the bottom of that page
5) find Windows "tools_r25.2.3-windows.zip" download and unzip it
5) find MacOSX "tools_r25.2.3-macosx.zip" download and unzip it.
6) In the SDK path replace the tools folder.

FIXED:
Unity versions: 5.4.5p2, 5.5.3p3, 5.6.0p3, 2017.1.0b3
SDK Tools have to be updated to 26.x.x