If you flushed a line, a recharge doesn’t always fill the lines correctly and residual flush fluid can hang around in the head. It usually clears up after a few pages, depending on the color being printed and the color affected.
Also a charge after a flush often leaves some bubbles. Normally the head and dampers will resolve those, but old dampers can get sticky and may let the bubbles move to the nozzles instead of bleeding it out - same symptom as a clogged nozzle, as no ink is coming out.. You might try printing something to get a little more ink moving through the lines to clear them out. If you only flushed one channel, you might try printing a large document that would use primarily the color you needed to flush (black, gray, light gray).
Just some thoughts. several other things that cause banding, such as paper advance adjustment, improper paper thickness setting. I’m guessing this isn’t the case since it doesn’t sound like anything changed, but you might double check.
