Miss fire

This may seem like a silly question but what octane fuel and spark plugs are you using? Sounds almost like a detonation issue especially if you have already switched out the ignition and are still having the same issue. May want to get a borescope and have a look to make sure there’s no damage inside the engine.

assuming good fuel and no engine damage Im very curious as to what would cause this issue for you so update once you figure it out. That’s a strange issue for sure. 

Are you able to give more history and detail:
Is this a new installation?
Is this a new engine, or one with some hours on it?
Has the engine always done this, or is this a problem which began after some use?
Are you flying when the problem occurs (I assume you are to get 195deg oil temp)?

While I cannot see why temp should make a difference, have you checked the trigger coil gaps? This can be done in situ, but you must use non-ferrous feeler gauges, as regular steel ones stick to the magnets, and feel as though the gap is snug when it is not.

Very interested to hear what you find, when you do.

The engine only has around 100 hours on it and I use  87 94 or 100 LL in it usually 87 or 94 I don’t feel there is any detrimental engine issues the leak down is 80/ 78 on all cylinders so it isn’t a detonation issue I have different ignition boxes on it other then rotax because it was doing it before with the rotax boxes on it and the ones I have can be used with a 12 volt battery also meaning they have an extra wire to energize them with just a battery in case the stator would quit and that is how I found out that it had to do with the stator. I bought a set of AC meters and hooked them up to each of the stator wires and when cool they initially produce the 30 volts but when it gets heated up to 195 cht the voltage will drop to 15 and then starts missing that’s when I switch on the 12 bolt battery system it’s hooked up to a separate switch, and it will start running smooth again. I initially thought it might be the rotax ignition but when it did it with these and I could introduce the 12 volt and it would smooth out I’m stumped. I also thought about the air gap why it would have anything to do with voltage curing it I don’t know but then I also thought maybe the magnets could be the issue maybe heat effects them that much, but I doubt it. I’m sure it is something simple as I could run it on the battery full time and it would never do it ,winter it was fine as long as the engine temp was below 195. There are a lot of people running the ignition boxes I do so I don’t think they are the problem and doing it with  the rotax ones on it pretty much clinches that thought. I’ll keep checking things and let you know what I find out.

Here's another thought for you:

The 'mag' switches in the cockpit need to be on for the ignition to fire.
When they are on, they connect to ground. This needs to be engine ground when running on the Rotax ignition commutators.
So if they are connecting to some other ground (eg hull ground) and there is a poor connection between that and the engine ground, it would effect the operation of the ignition modules.
How that might tie in with temperature, I don't know, but it would explain why you can run okay on battery 12V (assuming the battery 0V has a good connection to whatever the mag switches are connected to).

My aircraft is all metal, and the hull is grounded,  but I do not rely on the hull to provide the necessary 0V to engine, instruments etc.
I have a 0V cable from battery to firewall, and wires or cables from there to instruments and engine etc (the engine is a cable to carry starter currents.)

(continued from above)
Do you have an oil temp warning light?