Anachronisms
In the introduction, Suburbicon is described as having a shopping mall. In the 1950s, they were called "shopping centers." The use of the British term "mall" in this sense did not begin to take hold in America until the mid-60s.
The Tonka truck on the Mayers porch was a model not manufactured by Cat Trucks until 1975.
Continuity
The tape on Gardner's glasses changes.
The blood on Gardner's face/shirt changes.
When Hightower visits Gardner in his office he is addressed wrongly as 'Lieutenant' multiple times although his Captain's bars are clearly visible and he was addressed with his correct rank in their first encounter earlier in the movie.
Miscellaneous
Near the end of the film Damon takes a bite on the corner of a sandwich. In the next shot the bite is in the middle.