Yamalube 2W is a semi-synthetic low smoke 2 stroke oil designed originally to be used with personal watercraft (WaveRunner). They were ALL injected with the exception of the super jet, and IIRC, some of the newer super jets were injected (may be wrong...haven't dealt with many superjets).
2W is good stuff. Leave it. Smokes a little bit less than Quicksilver does too. Quicksilver is cheap oil. Thats why its popular. I remember buying a gallon at the dealership for under $8 many moons ago.
Unless the injector was run out of oil, or run upside down, both of which would introduce air into the pump, it will be fine. Now if it gets air into the pump, the pump will no longer move oil and that's where the problem is. Roughly 90-some odd percent of oil injected engine failures were/are caused by air getting into the pump somehow. Normally run out of oil at one point and the feed line gets a bubble in it. Most of them have a bleed screw to bleed the pump. I've never seen a pump actually fail unless it gets air into it or the tank is filled with something other than 2 stroke oil. When I serviced personal watercraft many years ago, we saw it all. We saw all kinds of stuff in the injector tanks. Gas. Diesel. Water. Oil. Dirt/sand. You name it. Manufacturers were just putting a little picture of I guess an oil pan. That little picture meant NOTHING to John Q. Customer. They just figured it meant whatever they thought it meant and that the dealer should warranty it when it's 5 years old and the oil tank is full of gas.
Now if you actually emptied the tank, there is a chance of having air in the system. I'd suggest bleeding the pump if it has a bleeder screw. I've not messed with a DT40 so I am not familiar with them. Perhaps someone more familiar with that motor can offer some help on how to bleed it. If not, call a dealer as they usually know-well the GOOD dealers do anyway.
Just because it's using oil now doesn't mean that bubble isn't still in the line waiting to find it's way to the pump. Or it's in the pump already and hasn't done it't thing yet. Bleeding it will solve the problem. Premixing keeps oil in the engine even if the injection is working. I used to run about 1/2 quart of oil in 9 gal of gas in my old bass boat-just for good measure.