Thank you for your review! That card you accidently skipped described told about why you ssometimes unable to use your detectives. Briefly - there are 4 stats: Strength, Attention, Communication and Energy represented by numbers in this exact order. Energy is how many times you would be able to use this character in a shift. So yeah, it's not a bug, characters run out of energy that's why you wasn't able to use them. I would've liked to make it more clear but unfortunatly had no enough time to do so