Sh. al-Albānī (رحمه الله) was asked whether optional deeds, in a general sense, are multiplied, and also evil deeds. He replied:

“There is no explicit scriptural-text (نَصٌّ) in the Divine Law stating that good deeds are multiplied, and likewise evil deeds with respect to the virtue of [a particular] place, or virtue of [a particular] time…virtue of a place such as Makkah or al-Madīnah for example…or virtue of a time such as this month of ours, this month of Ramaḍān.

There is no explicit scriptural-text regarding good deeds or evil ones being multiplied. However, some scholars say, by way of deduction (اسْتِنْبَاطًا), that they are multiplied…by way of deduction i.e., not [based on] a scriptural-text but only independent reasoning (اجْتِهَادًا), so if a person says: “good deeds are multiplied”, there is no harm in that because it is the view of some scholars, however it is not permissible to be definitive in that regard.”

Source: Jāmiʿ Turāth al-ʿAllāmah al-Albānī fī al-Fiqh (10: 109).