In case anyone runs into the same issue I did:
Problem: I added a new unit and the new unit never showed up after two days of trying. During that process I changed the IPs of my existing units (reserving them in my router) at which point none of the units showed up in HA at all even after deleting and re-adding the integration. The Kumo Cloud phone app worked fine for all the units the whole time.
Solution: I had to re-add the integration with “Prefer Cache” checked. Next I edited kumo_cache.json in my Home Assistant config dir, changing the IP addresses for my older units as needed (just search for “address”). Then, I saw that my new unit was in the file but didn’t have an address, so I manually added an “address” entry with the correct ip address below the “label” entry for that unit in the json. I knew it was the correct unit because the unit’s kumo adapter had the mac address listed on a sticker and I searched for & found that mac address in the json.