What could be causing our cedar siding to be warped near the chimney?
I will give a bit of an answer on what I see. It looks like the siding is taking on the salts from the masonry cement. The brick gets wet during a rain, the cedar that touches the masonry cement wick up the moisture from the brick which always has minute traces of the salt in it from the cement. Check out efflorescence This is what looks like in on the faced of the siding to a degree. Then it may be just blistered paint.

This is why the question of, "is the chimney added later" If it is, then the masonry cement while it was being built, cannot be cleaned off, and is in direct contact with the wood of the siding. If the chimney was original, there is a good chance, if the builder did it the way it is supposed to, the brick was laid first and the siding was run to the brick, keeping the cement away from the siding, albeit very close still, but still not touching the way a later added chimney would.

As mentioned before, it may only need what a good painter can provide, scraping, cleaning, priming and finish paint. To do it so it does not come back for certain, would require the removal of the siding, a small piece of flashing set to the brick, enough to nail to the subsiding and over the brick just enough to cover what the siding may touch. caulk the flashing to the brick, and caulk the siding to the flashing. Paint it up. Good till the cows come home.

Another way to accomplish that is to cut the siding with a circular saw set to depth so it does it cut ONLY the siding. The cut can be made as close as 1 1/2" from the brick, eliminating the need to replace the siding. The flashing mentioned earlier, now needs to be wide enough to go under the edge of the cut siding, and still reach the brick. After that is set, cover it with a piece of trim thick enough to have the face of the new trim just a little in front of the thickest part of the siding. Perhaps 1" thick...

This has become more than a  bit......

7-9 edit

To elaborate on the comment about the sun on the west side. The sun will draw out the moisture more rapidly on that side and therefore, expedite the depositing of salts on the surface of the siding. It goes like this, the brick gets wet and with that the salts in the brick or masonry cement, in trace amounts get sucked into the end grain of the wood siding. when that occurs, the siding swells which will start hairline cracks in the paint. This allows the moisture to get carried through the grain, and evaporate through the crack in the paint. This helps push the paint off the surface of the siding and make it bubble. The salts traveling with the moisture are deposited behind the paint as well as some leech out through the cracks in the paint too.

This is repeated each time the chimney gets wet from rain or melting snow and compounds the deposits formed the brick. The sun drawing it out on the one side more readily makes it even worse. In masonry, moisture is always seeking equilibrium, as the sun dries out the surface, the remaining moisture within the chimney moves toward the dry area, but since it is drying out faster than the other side....  Well I hope you see the point I am trying to make.