This thread may be covering or confusing 2 separate issues.
With 1 set to "SBU" and 19 = 20, my Growatt will bulk up to about 0.5V below 19/20, then kick into float mode. It actually never reaches 19/20 but stays about 0.5V below. I dunno why it stays 0.5V below the setpoint but since that is the case I have compensated by tweaking 19/20 up. I.e., I have 19/20 set to 57.7V and it actually charges to about 57.2V, occasionally hitting 57.3V. As long as enough solar power is available, it'll maintain 57.2 or close to it, with the charge automatically increasing if the load increases.
Note that with 1 set to "SOL" charging works differently. I prefer "SBU," though it depends on your goals.
BUT ..... as described in post #6, occasionally first thing in the morning, after the battery has partially discharged during the night, the Growatt will not recognize the solar power as the sun comes up. The Growatt will say 0 volts solar and 0 amps solar even though the sun is hitting the panels and I verify there is PV voltage with a multimeter. It's as if the solar side of the Growatt has "gone to sleep." So far the only way I have found to "wake up" the Growatt is to power it down, then power it back up. Then it immediately recognizes the solar side and starts charging normally.
I suspect this problem of the Growatt's solar side sometimes "going to sleep" in the morning is a software bug. So far it has happened to me twice in the one month that my system has been running.