The research and development effort went way over budget, the first couple rounds of production were fraught with difficulty, and the platform itself has design issues from being a “one-size-fits-all” compromise (despite also having variants for each service).
I haven’t heard anything particularly bad about the software effort, other than the difficulties they had making the VR/AR helmet work (the component never made it to production afaik).
They oxygen delivery system fails and has left pilots hypoxic.
https://www.nwfdailynews.com/story/news/local/2021/08/02/f-3...
The electrical system performs poorly under short circuit conditions.
https://breakingdefense.com/2024/10/marine-corps-reveals-wha...
They haven't even finished delivering and now have to overhaul the entire fleet due to overheating.
https://nationalsecurityjournal.org/the-f-35-fighters-2-big-...
This program was a complete and total boondoggle. It was entirely the wrong thing to build in peace time. It was a moonshoot for no reason other than to mollify bored generals and greedy congresspeople.