"Concentration problems" refers to difficulties in staying focused or paying attention. It means having trouble concentrating on tasks or keeping your mind from wandering. Full definition
Counselors treating children with concentration problems face a tough task. (allpsychologycareers.com)
Some people prefer receiving brief help to facilitate a decision that has been draining their minds, causing loss of sleep and concentration problems at work, home, or school. (michelelane.com)
«For instance, insomnia may lead to fatigue, which in turn may cause concentration problems that feed back into insomnia. (sciencedaily.com)