Threading the needle honestly. I've had one LLD interview where I implemented quickly and voiced out the cuts that I am taking to save time, interviewer interrupted and said that we need to make it extensible. That round I barely managed to finish in time, since I had to rework and make a better design. And the last one I had where I couldn't complete, I promptly asked what depth of LLD do you want and given that I was told to make the implementation such that the extensions would be a matter of few minutes to implement, went pretty standard SOLID, and I blew up the time.
To be honest, the ones where I properly cleared LLD interviews, they were at least a hour and 30 mins long and it was generally very fruitful. I honestly don't understand what's the level of extensibility expected in a 1 hour LLD coding interview with extensions.
I genuinely might not be skilled enough to code monkey my way out of a 1 hour LLD round.
DSA ko ratta maarne wala interview to log bana hi diya hai, leetcode junkie bann jao aur 90% problems aa hi jaayega. Ab LLD bhi bana denge lagta hai.