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I think it could be a blockage and causing stuff to back up or blockage was Unblocked causing more flow.
The water must be either in the sump or the direct tank. obviously depending on your setup a leak would be noticed.
2.Possible that the return has a blockage somewhere and isn't pumping enough water into the tank but that would mean that the sump should be more full correct? Coming down at the same rate but not going back up at the same rate so not sure why there would be less water.Check the line going from tank to the sump, not from the sump to tank...blockage could be a wandering snail