Same thing here. With no solar, just doing 50-90s, my Wets get back to 90% in AH but get very low in SG. Also when on solar but not ever getting to full by sundown. SG in Red or White, not in Green even if AH is not too bad.
Only cure is time at high voltage as the OP has described, to get the SG back to "true full" and start over. Various techniques are available to achieve that. On solar, if the solar controller does not have a voltage adjustment that lets you sit at high 15s long enough then you can by- pass the controller and do it that way.
But you have to do it. Those who never have a problem with all this according to them, either do not own an hydrometer or are delusional.