When you read your thesis before submission you’re trying to make it better. Each draft moves your research towards a better state of presentation. Each revision helps you tell the story of your work in a more polished way. You want to find typos, unclear writing and places that need a little help.
When you read your thesis after submission you’re trying to prepare for the viva. Each time you read moves you closer to a state of being ready. Every minute of careful reading helps you build yourself up for discussing your research with your examiners. You don’t want to find typos, unclear writing or places that need a little help!
So don’t look for them. If you find them, make a note, but focus on what matters. Focus on the flow of words and ideas. Focus on what you set out as important.
To help the transition between the periods before and after submission take a break. Leave your thesis alone for a few weeks, if you can. Come back to it with a refreshed mind. Take your time and read it carefully.