Originally Posted by Ollay

I think it's most likely due to the recent Core update. Lots of people reporting huge drops in traffic in the past couple of weeks, myself included. I was at 100K clicks per day then on the 21st November it suddenly dropped to 400 per day, no manual actions or anything.

Probably just a coincidence that this happened around the time that you switched to HTTPS. Hopefully it sorts itself out in a few months