If your feedback says "There are issues with your paragraphing and sentence structure".
Your tutor may be trying to help you to improve the structure of your writing. Often in this situation students are writing in very long sentences, or not grouping topic appropriately within a paragraph.
Answer
Context
Feedback about sentence structure and length are often to do with incorrect use of punctuation, but can also be about proof reading. Whereas lack of clarity in your paragraphs can often be about how you are planning your essay structure. Ask yourself the following questions; do I have a clear point in each paragraph? Are my paragraphs very long?
See the tips and resources below to plan some improvements in time for your next submission: 
- Sentence Structure Toolkit.
- If your feedback implies that your sentences are too long, revise our Should I Start a New Sentence page.
- See the punctuation page for help with commas and full stops.
- For help with paragraphing, consider the "Three voices" tutorial for support with what to include.
- Lastly see our How to Structure Your Essay tutorial for support with what to include in each paragraph.