The issue is that you are applying the max() function on a set containing only i - and then printing the result - every time you find a matching value. One way to rectify this is to create an initial set, matches, and then every time you find a match, add it to that set. After you've finished searching the response for matches, you can then use max() on this set and print the result.
Something like this:
def get_assets_for_group(ip):
decom_match = str(ip)
url5 = server + path1
response = requests.request("GET", url5, headers=headers, verify=False)
data = response.json()
matches = set()
for i in data['resources']:
url = server+path2+str(i)
response = requests.request("GET", url, headers=headers, verify=False)
data = response.json()
if decom_match in data["ip"]:
matches.add(i)
if matches:
print("Match found!", max(matches))