Actually, you might try the enzyme cleaner, leaving it in. Once it has dried out then try the OdoBan again. Do you have soda water you can use to fiz it up first?
Are you using the Odo-ban concentrate? You might need to use less water. I use to use it straight. I suppose the soda water mixed it up some.
LOL,. you obviously have experience in this area. I'll have to get some soda water. First I have to wait for night fall to use the stink finder.
Unfortunately too much experience. All four of our cats had urinary problems. I wasn't joking about using your nose. 
If you suspect cats from the outside have started this you might want to check outside the sliding door for odors. If you find any spray the area with a cat repellent.
If your cat/cats continue with this I suggest talking to your vet about running a sterile urine test.
Well, I think I've figured out at least part of it. There is a window up high in this room that is even with ground level - where the cats and they neighbor dog sometimes sit. It looks like one of them sprayed on the window. I cleaned that and the carpet below it. I won't know if I got it all until after dark when I use the Stink Finder, but it's better. This actually makes me happy. I would rather have it be in reaction to something than a medical issue.
On the upside, the stray cats haven't been around lately and the neighbor dog hasn't either. So, I'm paying a lot of attention to both girls and think I may be able to get rid of the smell tonight.
The room needed to be cleaned anyway, so this may turn out to be a good thing after all....