There is a known bug where the check in thing doesn't automatically pop up upon sign in anymore, which could potentially cause people to forget to check in despite having logged in during that day.
There is, frankly speaking, no way for the mods to know whether the players who claimed they have manually checked in are speaking the truth, or if they simply got caught in the above mentioned bug and therefore have not checked in during the day as a result(there are also a few player who admit that they missed check in as a result of it, disproportionately few actually, so tbh I'm sure at least some of the people who are claiming they have done manual check in is lying). Thus far, no one have provided any evidence that they have checked in during the previous day like they said they did, not that I expect anybody to be able to considering we should be expected to know when bug is about to happen.
Personally, I'm going to start screenshotting my check in page after I check in every day, so if a previous day becomes unchecked for some reason, I will have evidence to show that I have checked in on that day. I suggest everyone to do the same, otherwise I'm sure the bug will be dismissed as a case of "he just forgot and is lying about it"
Considering that there are more and more reports every day, the bug should still be on-going, so it's not too late to start creating evidence.