Facebook Group Doesn't Appear In The FB Search Anymore

My Facebook group was almost from day 1 getting larger and larger. It has been out there for more than a year and reached more than 30k members. However, for 2 days there was a sudden drop in the new members. I also realized that It does not appear when I search for the keyword with another fb account. I also delete the spammy content posted in the group almost daily. There is also not a competition or something for that specific keyword. What could be the reason for this sudden drop in the members and also disappearing when I search with a new account?