Do you have any unused controllers connected? Usually accidental input from any connected controllers that might have reset the throttles back to Idle.
Do you have phantom inputs from your keyboard? F1 usually don’t do anything so it’s easy to not realise it, but if that button’s acting up, then it might feed the sim with IDLE command without you realising it.
Best thing to make sure is to only have the necessary controllers connected to your PC. So bare minimum would be a mouse and your thrustmaster HOTAS. Everything else should be disconnected whenever possible.