Compiling integer varies from previous IDE version
In 1.8.6 it seems to be bad, not in range -32768..+32768
At least when compiled to Arduino Nano.

Simplest check:
void setup() {
Serial.begin(115200);
}
void loop() {
for (int i = 30000;; i++) Serial.println(i);
}

And another check with even more strange behavior:
void setup() {
Serial.begin(115200);
}
void loop() {
for (int i = 33000;; i++) Serial.println(i);
}

In version 1.6.5 everything OK.