Salad is one of those interesting things that can cause all sorts of problems. One thing that many people forget is that salad needs washing and often this is done under the kitchen tap. Depending on where you are in the world, you could be introducing bacteria to your meal from the tap water. Consider old pipes, old infrastructure, does the local pumping station need to be dosed with a sanitiser (ie chlorine), are you in the tropics where giardia is often present in the water supply. (Also note that the treatment for giardia is the same treatment for pouchitus ie metronidazole)

The other thing to consider about salad, is the dressing. I have a reaction to Palm Oil and, because it is cheap, many companies are substituting this in the manufacture of many food products such as instant coffee mixes, salad dressing, sauces etc.

Is a specific in the salad causing a problem? You may have a mild allergic reaction to one item that, without a large bowel, causes the flow to hasten through. (shellfish, such as shrimp, takes the rapid route of 3 minutes from hitting my stomach to exiting...seriously!)

Final thought is use of a binding material. If I have a meal such as a salad, I will also try to include a side dish of pasta or rice or even a heavy dough bread, to help bind the other parts of the meal into a more solid mass which then slows the motility down.

I thought I did.

I've had my ouch for 18 years and never had a problem with this until the past two years or so. I use Imodium more often now (never ever used it before despite being advised to), and watch what I consume. Sugary foods or drinks are usually the culprits. 

I have had a j pouch for thirteen years and the nightly problem for at least 10 years.  Having a good bowel movement before going to bed and stopping your eating after 7-8 pm is helpful.  I'm taking  a 4 billion probiotic that I have purchased from CVS which also helps.