CAUTION: SLIPPERY FLOORThe Arduino Library Manager installs the ArduinoJson version 6 by default.
However, using version 5 is highly recommended because version 6 is still in beta stage.
Open the Arduino Library Manager and make sure that ArduinoJson version 5 is installed.
It’s been fixed on May 27th by arduino/[email protected] and arduino/[email protected]. Unfortunately, version 1.6.6 only includes modifications up to May 19th, so the fix is not available through the Arduino Boards Manager.
They are located here on Windows: