So yeah, like Jack says, supply comes in from lower left: red hot, black hot sharing neutral. The upper right is switched-hot to a lamp.
The upper left carries switched-hot to a lamp, but it also carries unswitched hot on black to other outlets downline.
Important fact: Neutrals don't have breakers. The entire concept is that the hot breaker limits the current that is possible on neutral. Neutral wires are the same size as the hots. The shared neutral arrangement is called a multi-wire branch circuit. Breakers 9 and 21 are both returning current on the same neutral wire.
"But wait a minute, Harper. If each hot is rated 15A, and the same neutral is returning current for both of them, doesn't that mean the neutral is flowing twice as much current, up to 30A? That's way too much since that size wire is limited to 15A." Bingo. That is exactly what is happening in your panel.
"So how is that thing ever supposed to work?" It relies on the use of multiple phases, and the simplest is the North American 120/240V scheme, with opposite poles. If the two MWBC phases are chosen to be opposite, then something cool happens. Imagine black amps as + amps and red amps as - amps. If black has "+" 15 amps, and red has "-" 10 amps, how much does white carry? +15-10 = 5 amps. Only 5 amps. In fact you can try any value for black or red 0-15 amps, and neutral never exceeds 15 amps!
However, this requires the black and red wires be on opposite poles. Let's look at how service panels are laid out.
Now if you look at how your breakers are positioned, it's perfectly clear they're on the same pole, because they're two rows apart.
This also totally ignores another rule that applies to Multi-Wire Branch Circuits: The handles of both breakers must be tied together so they are shutoff together. It does not matter if they trip together, but any scheme that ties them will make them trip together most of the time.
So, the breakers need to be rearranged and replaced with either a 2-pole breaker (Siemens), or you must obtain a Siemens/Murray handle-tie. Then, you must rearrange the panel so the 2-pole or tied breakers can be on adjacent rows in the same column.