Sticking of KWC DOMO model faucet.

Probably needs at least one new rubber seal, you'd probably contact your supplier.

Various spare parts are shown in this manual (attached):

Does if have a sprayer and is it still hooked up?

mixing chamber of the faucet may be cracked

My bathroom faucet handle (not same brand as yours) was so hard to turn that it pulled the base around with it on the vanity when I jerked it. I used an Allen wrench to take out one of the set screws holding the handle on, put the tiny straw of a WD40 can in the set screw hole, squirted WD40 inside the handle, replaced the setscrew, and worked the handle to and fro a few times to lubricate the inside. No more sticking!

lowes home improvment

Yes, go to HD or Lowe's and buy a new one.
Be sure to take the old one for comparison.

Take off the aerator from the spout (it just screws on, and should not be so tight you need a wrench) and then run the water. You'll probably find the aerator screen is clogged with debris and you can wash it off. This often happens when you turn the water supply off to connect the new faucet. After you clean off the aerator and screw it back into place your new faucet should work fine.

Have the same issue. No one seems to have an answer, including KWC (except to buy a new $90.00 cartridge).

I would definitely take it apart to find out what is causing it to bind, that is not normal. Make sure that you turn your water supply lines off under the sink, via angle/strait stops. From under the faucet there is one or two nuts fastening the faucet to the counter, they are usually screwed on just a little more than hand tight. The problem may not be fixable, so be prepared to replace the faucet.

Having installed and fixed kwc domo faucets for years I'd probably take the spray head off of the hose, then look into the bottom of the spray head and see if the check valve is still there. It probably is. I used to use a thin screwdriver to pry the check valve out out.It will come out. You need to work at it a bit but these hold back a lot of water pressure and catch any crud coming down the water lines.
TL