LG Gas (Propane) Range + Double Oven resets during preheat, bottom oven only

LG LTG4715BD.BBDELGA Gas/Propane range/double oven

Long story first.. 6 months ago, bottom oven in convection bake started to smell strange, similar to plastic burning. We were really busy at the time, so we stopped using the bottom oven and switched to the top instead for awhile. After a few weeks, the top oven started to smell a bit like propane.. so we let it sit until we had more time for a service call. A week later, we had a local appliance repair person stop in, check all fittings (which were fine), remove several panels and take out some burned-to-a-crisp pieces of junk near the burners that shouldn't be in there, like twist ties, zip ties, etc.

Figuring the issue was resolved, we started the top oven to test and everything is perfect. Great! We turned on the bottom oven in convection bake mode, and it starts to preheat but shuts off with a chime after 15-30 seconds or so. No error messages or anything else visibly wrong. Run the diagnostics in the LG ThinQ app, and it returns a "Convection Fan" failure. Attempting to preheat the convection bake on the bottom oven confirms the convection fan does not turn on at any point before resetting prematurely. Seems fairly straightforward, right? However, turning on the bottom oven in regular bake mode also causes the same premature shutoff with chime. Attempting to run the smart diagnostic results in no errors found, but only sometimes. Haven't found a consistent way to reproduce the error, but it will 100% consistently fail to preheat and then reset itself.

TLDR; Top oven works fine, bottom oven always resets during preheat in both convection and normal bake modes.

Anything I can do to further troubleshoot or diagnose? Any suggestions on what could be the issue before we break down and call for LG flat rate repair at $349? Thank you!