Catalyzes the dephosphorylation of 5-amino-6-(5-phospho-D-ribitylamino)uracil, also known as ARPP, but has no activity toward flavin mononucleotide (FMN) (PubMed:27490826). 5-amino-6-(5-phospho-D-ribitylamino)uracil + H2O = 5-amino-6-(D-ribitylamino)uracil + phosphate kcat is 0.13 sec(-1) for 5-amino-6-(5-phospho-D-ribitylamino)uracil. Optimum pH is 6-8. Optimum temperature is 40-50 degrees Celsius. Homodimer. Belongs to the HAD-like hydrolase superfamily. DOG/GPP family.