A question about “fluctuating” vs "fluctuated"

The following sentence is a sentence in my composition, and I think it is reasonable to write a sentence in this way. However, a grammar checker has said that I should use "fluctuating" rather than "fluctuated". Is it a false negative check result?

Except for the amount of goods transported by railway fluctuated over 28 years, a significant increase can be seen in the number of goods transported by other methods.