You've reached the right place for help. I can see how frustrating it is not being able to see statements from April to August. Don't worry, I'll help get you back on track.
Occasionally this can happen if there are connection faults with the bank account during the periods or potential background issues with the bank during the download times. Since you know the dates of the missing statements, you can manually upload them by clicking Banking from the left menu and navigating to File Upload. From here you can manually upload the csv files of the missing months. You'll have the option of either downloading a CSV file of your missing transactions from your banks website (You can select a specific date period or delete any transactions from the csv file to only show the missing transactions) or you could just create your own csv file on excel for the missing transactions