When a process attempts to connect to a particular IP address, Little Snitch uses heuristics (based on previous DNS lookups, Deep Packet Inspection and more) to determine the corresponding hostname for that IP address, so it can figure out which of your filter rules shall be applied.
In some rare cases this approach may be unable to find a unique hostname match for a given address. The connection alert will then only show the IP address for that connection, often together with a list of possible hostnames which all resolve to that same address.
By default, Little Snitch uses the server name that a process sends only if it matches a DNS lookup it has seen. Some apps, such as Chromium-based browsers, do their own DNS lookups that Little Snitch can't see, so correct names get rejected. If you trust the processes on your Mac, open Settings > Security, click the lock and turn off "Verify server names asserted by process" (not available in Little Snitch 5).