One of the biggest problems in IELTS essays is a lack of logic. IELTS Task-Two essays requires a detailed and coherent argument. This means it must make sense!
At this point, I have to mention the dangers of memorisation. Students often memorise phrases and sentences, and put these pieces together pieces. These are usually from the ‘magic IELTS books’ [See ‘The Magic Easy Answer Everything Book’ series], meaning that the authors themselves are corrupt and dishonest, and usually not good writers. The end result can be a complete lack of logic. Entire essays make no sense! The result would be IELTS 4.