Chaining up of the devils in the month of Ramadan is mentioned in narrations in both Sunni and Shia books which means that devils will not be free to mislead people as they usually do in other months, that is why the numbers of worshiping Muslims ( fasting, praying and giving charity etc) are much more in this month of Ramadan compared with other months. Chaining up the devils does not mean that no sin will be committed during the month of Ramadan, but it means that decreasing and restricting their influence on many Muslims.
'Wassalam.