I've used online reporting since 2015 and my checklist for ensuring success (assuming their intranet is actually working) is:
1. Use IE. Chrome and everything else are problematic - the problems vary depending on hardware used, software version, and everything else including which way the wind is blowing on the day.
2. Before you start, check popups are enabled, clear the browsing history, disable or bypass any VPN.
3. MOST IMPORTANT - clear the IE browsing history AGAIN before submitting a page or proceeding to the next page.
4. Use ALL the dropdowns. If a dropdown freezes or is unresponsive (usually the nationality), CLEAR THE BROWSING HISTORY yet again and the dropdown will usually function.
5. For the first time yesterday, the nationality dropdown froze on me while checking my report status - I simply cleared the internet history/cache and it worked fine.
5. If it all goes tits up, have a coffee, go back and start again, do not pass GO, and do not collect $200.