This Unexpected error is often caused by a large number of cache piled up on you browser. I suggest performing some basic browser trouble shooting steps.
The first step to isolate this is to access your account through a private browser or incognito window. This is a good place to start the troubleshoot since this type of browser doesn't store cache.
You can refer to the following keyboard shortcuts below:
Google Chrome: Ctrl + Shift + N
Microsoft Edge: Ctrl + Shift + P
Firefox: Ctrl + Shift + P
Safari: Command + Shift + N
If this works, go back to your original browser and clear the cache to make sure your browser functions more efficiently. Otherwise, you can try other supported browser to help narrow down the cause of this behavior.
Trying to fix a ,bank reconciliation discrepency gives "Unexpected error occured try again later" for last 3 days?
Thanks for sharing your concern here in the Community, @1st Choice.
I'm here to help ensure that you'll be able to reconcile your accounts successfully in QuickBooks Online.
The error that you received when reconciling your Amex bank transactions can be caused by the stored data on your browser. To fix this, I recommend performing the troubleshooting steps shared by my peer Charies_M above.
However, if the problem continues, I suggest reaching out to our Customer Care Team. This way, they'll be able to investigate the root cause of this matter and apply a fix.
To do that:
Click on Help at the top menu bar.
Hit on the Contact Us button.
Enter a brief description of the issue in the What can we help you with? box.
Press on Let's talk.
Select on Geta callback.
Key in your contact details, then tap on Confirm my call.