The phrase "on multiple occasions" is correct and usable in written English. You can use it to describe two or more instances of something that has happened. For example, "She has apologized on multiple occasions for her mistake."
I said on multiple occasions.
He repeated the claim on multiple occasions.
"We've been at Worcester on multiple occasions.
On multiple occasions, Kaine was interrupted with chants of "USA!
The police were called to the home on multiple occasions.
The truth is, the NHS saved me on multiple occasions.
He has been recognized for exceptional teaching on multiple occasions.
And Figures testified Sessions called him "boy" on multiple occasions.
The grossness emerges on several levels and on multiple occasions.
It occurs not just once, but on multiple occasions.
Even so, talks almost collapsed on multiple occasions.
Since I tried Ludwig back in 2017, I have been constantly using it in both editing and translation. Ever since, I suggest it to my translators at ProSciEditing.
Justyna Jupowicz-Kozak
CEO of Professional Science Editing for Scientists @ prosciediting.com