What is the best word to describe popularity that does not stay the same through the years? [closed]

How about ups and downs? From Lexico:

ups and downs (pl. n.): Rises and falls, especially in the value or success of something.

From M-W:

ups and downs (pl. n.): alternating rise and fall especially in fortune

Another possibility is rollercoaster ride. From Lexico:

rollercoaster ride (n.): A journey or experience of extreme and rapid changes.

Both answers could work, depending on the context, but I would say ups and downs works best for your "movie" example.

Addendum: Many thanks to @JasonBassford for pointing out that the OP has added an example sentence. The OP's example sentence with the answers suggested above:

The movie has had its ups and downs (in popularity) since it was first released in 1982. It became a surprise box office hit, but suddenly after a couple of years it slid into oblivion and it was not until the early 2010s that it regained its popularity."

The movie has had a rollercoaster ride (in popularity) since it was first released in 1982. It became a surprise box office hit, but suddenly after a couple of years it slid into oblivion and it was not until the early 2010s that it regained its popularity."

How about the word "fluctuating"?

In vocabulary.com, it gives:

Fluctuating describes something that has unpredictable ups and downs. Fluctuating often refers to changing numbers or quantities of something, like fluctuating stock prices that go up and down.