It looks like Sunsunk has some issues with a service on their side. It manifests in the inverter not charging/discharging according to power settings. When you check the app, it gives all kinds of Service error and/or shows your inverter as offline. If you check the date on the inverter itself, it shows 29 Feb and some other time than current.
Workaround: Disable timesync on the inverter and set the date/time to expected values until the issue is confirmed resolved on their side.