Major INDI Library release v1.9.0 bring significant internal changes championed by @pawel-soja to modernize core INDI Library drivers and clients. New drivers for DeepSkyDad Flat Panel & Pegasus devices plus further improvements to PCM8 drivers.
After a fresh installation of Ubuntu MATE (20.04) the problem seemed to persist.
After installing Raspberry Pi OS, Ekos had no issue finding the camera. And everything seems to work as it should.
Considering Ubuntu MATE for the Pi 4 is still in beta I'm not sure who's end this issue is coming from.
At any rate, its worth noting that other devices (Celestron SCT focuser and Celestron CGX mount) had no issue connecting under Ubuntu MATE.