I have found this link, can you open it? https://english.stackexchange.com/questions/60579/some-singular-vs-plural

I think it is a shortening of the phrase 'There must be some sort of mistake.' 'Some' can be used before an adjective when you don't know everything about the noun. For example: "I think it is some sort of tree", "There was some weird guy standing there". In casual speech, sometimes people use it before a noun as well. I hope this helps!

Some can can be used with a plural - as in 'I'll have some of those oranges, please', but doesn't have to be. It can also be used when the exact number of the thing(s) being referred to is unknown, or is not relevant. So here it is referring to something unknown, an unknown mistake or mistakes, whether it's one or more is not important.

because they did a mistake in the subtitle :)