When the cameras base rate is set to 23.98fps you are going to be monitoring at 23.98fps. Meanwhile the sensor in S&Q 48fps is running at double the monitoring rate, so you will only see every other frame while shooting so you may not see the flicker. This would be true of any camera set up in a similar fashion.
When you play the clip back it is slowed down to 23.98fps, so now you do see every frame and will see any flicker.
I always recommend that if shooting S&Q that after the first shot you do a playback check for exactly this reason.
Alister is so right - especially in these days of LED lighting fixtures, it can be very easy to have flicker problems even when you are doing everything "by the book."
I was recently shooting with some theatrical LED lights - 60Hz power, shooting 60fps at 29.97p for TV - so I put in a 1/120 shutter - seems brain-dead simple. But on playback there was flicker on the LEDs... turns out a 1/100 shutter worked, even though everything was labeled 60Hz...
If I hadn't checked playback, I wouldn't have realized until it was too late. And that applies to Epic and Alexa just as much as Sony cameras - always check playback.
It also helps to watch a waveform monitor - it will sometimes show you flicker that your eye is missing.