There is something going on with the resistance change in your build. Resistance is rising far faster than it should be, which means that there is a hot spot in one (or both) of your coils, or a coil lead that isn't making a good electrical connection until it heats up or maybe a hot leg that's about to pop on you. Your chip is reading the resistance change, calculating what the temperature should be given the starting temp and resistance, and then changing the power accordingly.
Remember, in the temperature control model on your chip, temperature is a calculated value. There's no device or sensor measuring temperature in the chamber. The chip is programmed to read resistance, compare it to starting resistance, use the TCR value for the coil's material and estimate temperature.
I always lock cold resistance if the mod can do it. Some people don't (I have no idea why; none of my business), and some mods just set the cold resistance to whatever it was when the mod first read the coil in a TC mode.
Separate issue: I can't get a very satisfactory vape at 350 F on any of my builds with SS coils (dual). But I don't have an OBS Engine (yet!). My TC run atomizers are two Battlestar RTA's, two Moonshot RTA's, two Goblin RTA's and two TFV8 RBA's. Oh, and two drippers. All are set between 420 and 450 F.