Usually the boredom phase comes, occurs when we experience repeated defeats. if I examine deeper, situations like this are in a slightly depressed state because the games we play don't give anything as we expect. for example, OP plays one slot game in each of his betting sessions. but every time we play, we never get a win. even though if we have to count, the money that has been lost in these slot games has drained quite a lot of our money. then, a feeling of surrender arises which results in boredom to continue the game session. because, our brain has processed that defeat for the umpteenth time will happen again. i'm pretty sure, if there are many who have or often experience such things as the OP said in this thread.
Referring to what you said, we agree that it all depends on the mood at the time. also, gambling bankrolls at that time. which in the end, creates boredom that affects our psychology. but based on what you've said, I think that this is another factor that can cause boredom to occur.