This is nothing that game providers are trying to hide from you, every game provider have a different time frame for how long the bonus can be saved without showing you the result.
Some providers doesn’t let you save bonuses at all, so they will credit the bonus win to your balance straight away if you close the game.
Once you have got a bonus in the game the result is already known by the providet.
For example hacksaw slots, if you don’t open your saved bonus within 12 hours (I think it is) then the wins from the bonus round will automatically be credited to your balance and the bonus round will be removed.