LG Gas oven, converted to propane. Model # LRG3061ST Electronic igniter replaced.

The problem is that the oven won't ignite to preheat or won't re-ignite to maintain the temperature during baking. The problem is intermittent - happens sometimes, other times it doesn't. If it fails to light during pre-heating it gives me an error code (F9 I think) which only means that it didn't heat up in a set amount of time. Once it reaches the pre-set temperature, it may not re-ignite to maintain that temperature (400 degrees, open door, put a pizza in, and 15 minutes later temp is at 250 according to my infrared temp probe). During all of this, the igniter will be glowing red hot, cycling on and off. No error codes will present if it is during the baking cycle. The igniter was recently replaced because it finally wore out, but the problem is exactly the same before and after the igniter replacement.

Now, here is a clue that I think narrows down the potential problems: if any burner on top is lit, then the oven works completely normal. It will preheat and maintain temps through the entire baking cycle.... as long as at least one burner is turned on. Could this have something to do with gas pressure?