[Chris is me]

Lots of things that could be going on here that could cause these issues, depending on a number of factors. What is the tooth count of your sprockets? How are you tensioning your chain? How long are your chain runs?

First things first, if you're breaking 25 chain in a drivetrain yes there's probably something you're doing "wrong" with it, but switching to 35 will give you a lot more fault tolerance so you don't necessarily have to solve that problem to keep going. In the interests of time and reliability, if you have the weight 35 chain might just be the easiest way to go.

I'm assuming you guys don't have any problems with alignment - that would be pretty easy to see.

If I had to wager a guess, if you're using 16T or 18T sprockets (the "standard" for 4" wheel WCDs for the past several seasons), but driving 8" wheels with them, this is probably part of the problem. Smaller sprockets with bigger wheels will be downstream from a larger reduction to get the same speed, so they are loaded with more torque. Shock loading is also more of a concern this year than other years. If you can make your sprockets larger, you will have less tensile force in your chain. In a WCD, you should be able to go up to at least 22T if I recall correctly.

Chain that isn't properly tensioned will have more problems - you're more likely to skip a tooth and shock loading will be greater, leading to a larger chance of chain failure. Chain on small sprockets connected to large wheels will stretch more quickly than chain on large sprockets or connected to smaller wheels, as a function of the increased load put on them. If you did exact center spacing with your chain to start, it might have stretched too much under load by now.