I have an Adafruit Feather HUZZAH ESP8266 board that I'm running arduino code on (ie: I'm compiling and running directly to the ESP8266 using the arduino IDE, no other boards involved)
About 350ms after starting the board, "loop" stops getting called, then at the 1300ms point "loop" starts up again. Originally I thought this was related to the servo library and posted it here BUG? Servos go to 0 during initialization for about 1 second? - Motors, Mechanics, Power and CNC - Arduino Forum
Since then I simplified the test to just printing out millis during loop (no servo, no wifi, no libs at all) and I still see the stall. Someone else confirmed the stall doesn't happen on an UNO. So I thought it would be better to post this here since this seems to be related to the port of the Arduino runtime to ESP8266 and doesn't have anything to do with the servo library.