I hade a issue with the smart load function on my Deye 8kw. there were a firmware update Wednesday 11/11/2020 and now there is not any issues.
In connection with the Geyser I will use a 2kw element on the geyser so if the is not enough power from PV so it do not drain yoyou must ur battery. On the inverter you must enable the smart load function, where you also set the state of the battery when it must switch of if the is no grid. The watt setting on smart load must bet set for a value bigger than your geyser element.