What are Rich Suds in Match-3 Elements? These are similar to regular suds where they'll spread to tiles if you don't clear them for each turn. However, they are more difficult.
Rich Suds (Source: Playrix.com)
In order to remove them, you need to clear 2 matches that are beside them, or use power ups. This can be very tricky so try to match similar colors together if you see this element.