I don't have any brains left to pick! 
Yes, I have had quite a few that didn't have ishoos over the years, but often it's the ones you work the hardest with that stick with your the longest, iyswim.
It's really only been the Boxer x GSD and Pip that have had problems - well if you don't count Lurcherboy's, thankfully brief, flirtation with separation anxiety when we lost Oldgirl last year.
The Boxer x GSD was rescued from a puppy farm. His father was an extremely nervous and aggressive, massive, GSD and the consensus was that his problems were genetic as a result - exacerbated by him developing panosteitis as a youngster and missing out of months of socialisation because he was too heavy to carry - and then our vet deciding to neuter him at 6 months. He was a very big boy and we tried for years to rehabilitate him, but in the end, although he'd improved massively, we went for management and containment over keeping-on putting him through so much fear and stress. So, we had a huge outdoor kennel and run for when we had visitors he didn't know (he was fear aggressive to people and dogs) and knew when and where to walk him to avoid any confrontations. We had him trained to the point he would completely ignore other dogs and people and could go offlead to chase frisbees and would still ignore them, but were always exceptionally careful about where and when we took him.
Oldgirl herself was a monumental pain in the rear as a youngster, but nothing unusual for a Border Collie x Belgian Shepherd. She was just very young, very highly strung, brimming with energy and too clever for my her own good!
She was an amazing dog once she'd matured and I still miss her sooo much. 
My Wheaten girl was rock solid, super brainy, easy to train and had her bronze silver and gold by the time she was 1 year old. We never had any problems with her, could take her anywhere and do anything with her.
First dog was a massive long-coated GSD bitch, that MIL found under a hedge and close to death while I was staying with them. She was awesome - almost a human in a dog's body really she was so intelligent and an amazingly calm and centred girl. She was so well behaved that dh and I managed to live in student accommodation, on campus at uni, with her without anyone realising! 
Second dog was a Lurcher, although we didn't know it at the time. She was a Whippet x Sheltie. Thick as bricks, really dizzy and super fast off lead, but very pretty and sooo sweet natured - loved nothing more than to jam her head under your chin and have a cuddle. Sadly she escaped from my Mum's garden when she was dog-sitting for us, was missing for 24 hours and was hit by a car and killed outright - ironically right outside the vets. She had somehow managed to cross the M42 motorway to get to where she was found.
It was having the Boxer x GSD with all his problems that got me interested in dog behaviour. If I'd never had such a difficult dog, I wouldn't know half what I do now about behaviour and training. Nearly every trainer/behaviourist I've ever met says the same about having a particular dog with issues that started them on the path.