It makes it difficult to keep hold of the reader’s interest.

or

It makes it difficult to hold the reader’s interest.

Your sentence needs a subject at the beginning. I used “it” but you could use “The confusing plot” or “The storyline” or something similar, so it would then read, ” The confusing plot makes it difficult to hold the reader’s interest.

Hope this helps.

Just spotted your addition. Simply place a comma after “spelling” and add your second sentence to the first.

i.e. That makes it very difficult to keep the reader’s interest.

The books contains too many big words, making it very difficult to keep the reader’s interest.

The book’s plot took convoluted twists, making it very difficult to keep hold of the reader’s interest.

I hope that helps.

This article is very obtuse, making it very difficult to keep hold of the reader’s interest

Ok….now after you added the details… Just add a coma before ‘making’, and add a connector such as ‘so’, ‘hence’, ‘thus’….

Just put a comma, not a period, before the word ‘making’ and it will be correct.

If you would rather have two sentences, start the second sentence with “This makes it difficult…”

try maintain.