Juraj:
it is not about the IDE version, but about the esp8266 SDK version used with esp8266 arduino core package version. there is some settings compatibility broken between the SDK versions. the SDK setting are on the flash
In the Arduino-IDE's "Boards Manager" I see "esp8266 by ESP8266 Community version 2.3.0 INSTALLED". And my Sloeber-IDE refers to "Location": http://arduino.esp8266.com/stable/package_esp8266com_index.json from which I am using the board "esp8266/2.3.0".
Doesn't that mean that I am using the exact same esp8266 SDK in both IDEs?
One difference is that in the Arduino-IDE I am using a CPU frequency of 80Mhz while I am using 160Mhz in the Sloeber-IDE.. (I want my device to run as fast as possible..) Also I am using a different upload speed: 921600 from the Arduino-IDE but only 115200 from the Sloeber-IDE..