The book of Nehemia states that the Israelis didn't keep Succot from the times of Joshua Binun (about 1000 years, Nehemiah.8.17.
וַיַּעֲשׂוּ כָל־הַקָּהָל הַשָּׁבִים מִן־הַשְּׁבִי סֻכּוֹת וַיֵּשְׁבוּ בַסֻּכּוֹת כִּי לֹא־עָשׂוּ מִימֵי יֵשׁוּעַ בִּן־נוּן כֵּן בְּנֵי יִשְׂרָאֵל עַד הַיּוֹם הַהוּא וַתְּהִי שִׂמְחָה גְּדוֹלָה מְאֹד׃
The whole community that returned from the captivity made booths and dwelt in the booths—the Israelites had not done so from the days of Joshua son of Nun to that day and there was very great rejoicing.
I also recall that the Torah mentions that they didn't circumcise for 40 years in the desert.
What are some additional examples of Mitzvos that are mentioned as "not practiced for a long period of time"?