Read your results carefully. That "4th Cousin" is actually described as a range of 4th-6th cousins. Yes, they do put it under the heading "4th cousin" but the descriptive range is 4th-6th. Similarly with other groupings.
I have found Ancestry to be overly optimistic in the closeness of matches. All of my confirmed results have almost always been at the farthest edge of the range (see below for exception). If Ancestry shows it in the 4th-6th grouping it will be at least a 6th cousin match. If it is in the 5th-8th grouping it is usually a minimum of a 7th cousin match, and has been as far as 9th cousin. Those 2 generations make a big difference! Going that much farther back in a tree can lead to areas where people have no ancestors listed.
Exception: I have a few cases where the match listed is a lot closer than what trees show. One is a 5th cousin match showing up in the 2nd-3rd column grouping. However, that match comes from a family line where there was some overlapping lines and intermarrying. Not close intermarrying, but along the lines of 2nd-3rd cousins marrying semi-regularly among various branches. This has probably "reinforced" or "doubled" certain strands of DNA making the matches look closer than they are.