Are you using a 30" or 40"?
Is yours with the new smaller smaller wood chip holder (not the loader) that the chips are dumped into?
It is hard for me to comment on the 30" since I only have a 20 month 40". From reading MES posts for almost 20 months, the most complaints about chips burning properly is with the 30". There is a lot of speculation as to why, one reason the heat element heats up the cabinet so fast the element does not stay on and keep the chips burning. I'm not sure that is the reason, 30" owners would know. It could be how close the chip holder tray is to the heat element. Mine is almost touching and the chip holder is warped from the heat.
Some possible solutions might be.
• Start with a few dry chips, if you preheated your MES you should have smoke in 2 to 3 minutes or less. When I say a few chips 6-10 small chips. Once the those chips are going wait about 5 minutes and add another small batch. In 20 minutes or so you will have a hot bed of chips and hot ash inside the chip holder tray. From that point on combustion shouldn't be a problem and you can add more like a half cup of chips. Personally I found in my MES the sweet spot is like 8 to 10 chips. Even if it is dark I can tell when the amount is right, the smoke smells great, it is sweet and no bitter smell, in the light it will be that TBS. Even if you decide to use soaked chips start the smoke with dry to get that hot bed of ash and chips. Wet chips usually only take another min. or two to start smoking. I switch to chunks after I get the chips going, no more than 2 or 3 chunks at a time. However chunks are not necessary, I use them to try and get an extra 20-30 min. of smoke time before adding more wood. Using 10 chips at a time I have to add chips every 30 min.
• Get a tin can and start a few briquettes, use 1 or 2 hot grey briquettes with the wood chips to get them going. Some MES owners swear by the use of briquettes, and say it adds a smoke ring on the meat as a bonus. I did the briquette thing for several months and the smoke ring only happened a couple of times, since I had no issue getting chips smoking I hardly use briquettes.
• Preheat your MES. Set the Controller to 270º and when it gets close start your smoke, quickly add the boiling water, add your meat, throw in the chips. That tray will be hot enough to start those chips for sure. Yes the manual says preheating isn't required.
How I got into preheating my MES. In the summer, temp recovery and getting up to temp hasn't really been an issue. When outdoor temps started dropping, the recovery times on the MES started increasing. But I noticed that after 3 or 4 hours in a smoke, recovery was always pretty fast 5 to 10 min. Even when the ambient outside was around 40º and once or twice colder (sacramento doesn't get below 40º very often). The only thing I could think of was all the metal was thoroughly heated, and the insulation was also storing heat. So during this time of year I preheat for at least 2 hours, and 45 min. to hour when the temps are warmer. I have kept notes and if I preheat to 260-270º , the temp drops to around 195-205º and 5 to 10 minutes later the temp as recovered to my desired 220-225º. If I only preheat to 225º depending on ambient, after meat is loaded the controller temp drops to 160-175º, it could take 1 to 2 hours to get to 225º.