You cannot have 'the book is being lost' or 'was being lost' You can have ' the book has been lost....' or ' the book was lost...'

We don't use the passive voice to say '[something] was being lost / is being lost". Use the simple tenses instead. The meaning of 'lost' here is 'missing' or 'not yet found'. My cat is lost. I want to find her. (simple present) My cat was lost. I'm glad I found her. (simple past) When we say '[something] is missing', the meaning is 'absence' or 'wanting'. The boy is missing his front tooth. I am missing my friend since she moved away. The soldiers are missing in action.

The difference between "the job is being done" and "the job was being done" is really easy to understand, I hope so. When you say the job is being done, you mean that the action is happening in the present and we don't need to specify who's doing the job (passive voice). And when you say the job was being done, you mean that someone was doing the job in the past. You need consider that when we say "something is/was BEING done" we put a lot of focus on the duration of the action. But when you say "something is/was done", we mean that we've got a result and something is finished.

The difference between "the job is being done" and "the job was being done" is really easy to understand, I hope so. When you say the job is being done, you mean that the action is happening in the present and we don't need to specify who's doing the job (passive voice). And when you say the job was being done, you mean that someone was doing the job in the past. You need consider that when we say "something is/was BEING done" we put a lot of focus on the duration of the action. But when you say "something is/was done", we mean that we've got a result and something is finished.

The difference between "the job is being done" and "the job was being done" is really easy to understand, I hope so. When you say the job is being done, you mean that the action is happening in the present and we don't need to specify who's doing the job (passive voice). And when you say the job was being done, you mean that someone was doing the job in the past. You need consider that when we say "something is/was BEING done" we put a lot of focus on the duration of the action. But when you say "something is/was done", we mean that we've got a result and something is finished.