Hi! I know it can be so frustrating during the baby & training stages. I remember very well. My advice would be not to let Thor have run of the apartment until he is much much older. A secure gated off area for now will help him learn & is for his own safety. When Bella was a puppy, she did well with potty training, but she would occasionally forget, especially while playing fetch with us.....all of a sudden she would have to go & in her excitement would go right there!
She was more interested in 'playing'. Good news:
it does get better with repetition, praise, praise, praise & the smaller area confinement. Thor is a cutie!