fallout shelter mysterious stranger when does he appear

Try levelling up the perk (This does require you being a higher level though).

You still have the chance to fail, until you have failed 9 times, in which case you have a 100% chance of success. E.g., You may start with only a 10% chance of success, but when ever you fail, that chance of success increases by 10%. Some games use a system that have a low percentage of success, but with every failure, increase the chance of success.

This is not the same as 'stacked chance'. I.e., there is nothing wrong with your game. That chance is fairly minimal, and is entirely legitimate that this can happen indefinitely. This means the game randomly selects from 10 choices: 9 'no's', and 1 'yes'. To elaborate slightly, what this means, is that every time he is eligible to show up, he has a 1 in 10 chance to do so. So it's a possibility that you've just been unlucky of late. Yes, this means that he should appear at least once every 10 times, but 'chance' doesn't make that guarantee. The thing about chance is that every occasion he can appear, he only has a 10% chance to appear.

Fallout shelter mysterious stranger when does he appear