When going into Admin > Submit Claim to HMRC, it takes around 3 hours for the window to open. When opened, there is one particular tax claim that has more gifts than the total amount of gifts in the database. When querying on this tax claim, the amount of donations do not match up with the submission grid.
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.