I do not know why int() on this integrand fails always first time, and works second time it is called. seems like something is not loaded correctly first time?
Here is a movie. it is few minutes long. This happens by random and not each time. This movie shows the command starting from "restart" are repated 4 times. First two times, no error. Then the error shows up. So it is random. Maybe it depends if Maple is busy with other things or not. I have each worksheet set to use its own server though. So I have no idea why this happens sometimes and not other times.