** To the folks
getting an error at the last step while submitting the online application (after successfully uploading the files) **
Below are my observations (It could be 100% spot on or totally wrong. Please don't quote me on this.

If you think it's not accurate, feel free to ignore my post):
- Signs that you would get an error at the last step (at the time of submission): After uploading the additional required and optional documents, if you refresh the page (or log out and log in again) and some or all of those files are not saved, there are high chances that your application will not be submitted successfully even after uploading those documents again.
- Potential Reason: If your details / file names / size / formats everything seems fine, there are chances that you have overlapping date/month entries for 'Work and School' or 'Immigration' or 'Residence' information or anywhere else in your application. (This point is more or less same as user ZZDown mentioned in previous post). So the error is NOT because of multiple entries but could be because of overlapping date/month entries (it could have happened indirectly because you have more entries). I mean to say even if you have multiple entries but if those are not overlapping in terms of date/month, you might be fine.
- Solution: Once you make sure that you don't have overlapping date/month entries in any of the applicable sections, in the Additional Required and Optional Documents section, if you refresh the page, your files would still be there. This could be the sign that your application will now be submitted successfully.
- Example: I made three entries in 'Work and School'.
- Jan-2019 to Nov-2019: Job 1
- Nov-2019 to Nov-2019: Unemployed (for 2 days due to job change)
- Nov-2019 to Present: Job 2
- At this point my additional documents were not getting saved and after uploading those again. I was getting error at the last step of submission.
- I removed entry 'Nov-2019 to Nov-2019' for 2 days of unemployment, now my entries were like below (which makes sense system wise because system asked the information with reference to MM/YYYY and not DD/MM/YYYY) :
- Jan-2019 to Nov-2019: Job 1
- Nov-2019 to Present: Job 2
- As soon as I made that correction, my additional documents were also saved properly (even though I refreshed the page) and I could submit the application immediately.
- As per the posts of Users ZZDown and destiny2016, they removed some entries (and added it in separate file). That would have indirectly removed overlapping date/month entries and resulted in successful submission.
- Conclusion: If you are not able to submit the application successfully, it's not (only) because of IRCC system bug. There are high chances that there's difference in the way you have provided the information / documents vs the way system expects the information. Reason could be same as mine or like it's mentioned by some other users. Now till the time IRCC enhances the online tool with better error handling and messages, you can double check, correct the required data and try to submit the application. It should go through.
Good luck everyone!