Yes, this has happened a few times not just on the site I am co-owning now but also on my general chat forum I used to have up until 2017. I would have weeks where I would get a lot of traffic, a lot of activity, even new members, then there would be a few weeks where it would be really slow or just no traffic or activity at all. It became frustrating when traffic would almost slow down to nothing as I was still doing what I always did to promote my forum and to help bring traffic in. I feel with any site, sometimes you are going to have those slow times no matter what you try and do and it's best to just keep going and don't let that grind you down, traffic will soon increase again and things will start moving again.