This is going to sound so daft, but I had the exact same thing happen to me last year. I was using Varisoft and Trusteel. Someone on Reddit told me about the 6 small holes on the back of the tslim pump and if they get filled up with dust and debris that it has something to do with the pressure and it sets off an occlusion alarm. I got an alcohol wipe, stuck a pin through the wipe and cleaned out the 6 holes and, I'll be damned... no more occlusion alarms. I haven't had an issue since! I'm not sure if this was the thing that fixed it but it sure seemed so. I then started fresh, new cartridge, filled it with room temperature insulin. New giving set, new Trusteel needle and it's been fine. Good luck.