Thank you for the response Genreve.
However from my experience it is not correct that the web app 'automatically refreshing' transactions fixes the issue with missing transactions. If that were true, opening an AccountRight file from the web app would automatically trigger MYOB to download the missing transactions. This doesn't happen though. The only way to re-download the missing transactions is to do it via the button provided in the desktop app.
The issue is that MYOB periodically goes through phases where it appears that transactions are not downloaded from the banks to MYOB's servers correctly. The 'Get bank transactions' button in the desktop app fixes this, because it sends a new request to download transactions.
Automatic refreshes in Business do not fix this, because it appears that the missing transactions have not been downloaded correctly to MYOB's database in the first place. There are no transactions to push to the bank feeds screen if the transactions are not in MYOB's bank end database to start with. The 'Get bank transactions' button seems to initiate a new download request from the bank, which then pushes the transactions to the MYOB file.
At the moment, the only way to bring in the missing transactions is to call MYOB support and have them manually submit a transaction download request for the specified period. Have had to do this many times. Refreshing the bank feeds screen in the web app does absolutely nothing. Very frustrating.