You're in luck, we identified this issue earlier this morning (well, morning for me...). The driver needs to store the support modes and fan modes in a JSON array, with each mode wrapped in double-quotes.
So I updated my driver for Mitz AC units. When you say Ecobee, is that a built-in integration, or a Community developed one? Or perhaps the more relevant question is, are you able to provide a screenshot of the device current states like I did on the linked topic? To see if the modes are being stored correctly?
