Our support team raised a ticket for us that they no longer see an external id field in the match by section in the import wizard:
Our customer claimed they see the external field in the match by section till last Friday.
I checked that external field. It has external Id checked by unique unchecked.
I tested that if I check the unique checkbox it will instantly work. But our business is not sure about whether we should do that.
I am a little bit confused because due to this article: https://help.salesforce.com/articleView?id=000002783&type=1 . The field should be unique in order to be shown in the match by section. I am lost in why our customer was able to see it.
My guess is it could be:
Salesforce was somehow forced the external Id to be unique but recently changed it.
External Id (not unique) was able to be used in data import wizard before.
But I didn't find any related document of that. I checked the version of the org and it is still Spring 17 so shouldn't be a big change last week. So I am still very confused.