Are health problems ever caused by over alkalinity?
Yes, but it's uncommon from diet alone. Metabolic alkalosis can result from prolonged vomiting (which loses hydrochloric acid), severe dehydration, or consuming excessive alkali. It would be difficult to become over-alkaline through food alone, though it is technically possible if a person ate only 100% alkalizing foods and no proteins or other acid-forming foods.
If your first-morning urine pH is consistently 8, this most often indicates a "false alkalinity" rather than true over-alkalinity — worth understanding before you change anything.