I had the same problem in a Interarms .375 H&H. I satisfied myself that the ejector wasn't the culprit but didn't go any further. Instead,I sold the rifle.
Recently I had a .375 Ruger built on an FN action. The same ejection problems cropped up. It turned out that the cases were hitting the inside of the receiver bridge as they exit the ejection port. The result was the loss of 'ejection energy' and the case just falling off the bolt face. Sometime it would fall to the ground, other times it would fall back into the magazine. Bad either way.
This kind of problem arises when using a fatter case than the M98 was designed for.
A trip back to the gunsmith to knock the upper corner off the right bolt lug race solved my problem. Ejection is now very good.
Here's a couple of before and after pictures on an action similar to the M98