It definitely happens. I'm in my regional chat very often at night, where, because of the relatively small number of active users, everyone has a good chance of receiving each rain. This means that every user present at night often receives several rains in just a few hours. This is the case for me when I'm not shadow banned, and then one day, not a single one for exactly 7 days. Statistically, it's impossible for this to happen by bad luck. It's really frustrating that Stake won't admit it.
I want to emphasize that in all cases, the known eligibility requirements are met!