I have seen this same searching issue with single characters in a text field. I'll be curious to see if this is confirmed to be a bug. In my case it happens across all Esri apps I use (Web App, Experience, Instant) and the searching layer is hosted in ArcGIS Online. I can't say if the problem also happens with an Enterprise-sourced layer.
There are only 2 workarounds I know of. Unfortunately I don't think either of these will work for you:
1) Tell the users to include other parts of the intended search result. In your case I don't think that will work given your lot strings. In my case the problem is a direction letter abbreviation in between address number and street (entering "3805 s casper" does NOT produce results, "3805 casper" does). So I have been able to live with the issue for now...
2) The problem seems to be created when you set up a full text index on the AGOL hosted feature layer. I have found that if you delete the full text index, now the search will work assuming the user enters the exact string. They will even be prompted with the candidate suggestions. This might work for you with the lot field. However, by eliminating the index you loose the enhanced searching. Also, when you configure a new search in the Esri apps (ExB, Instant) a new full text index will be created automatically by AGOL when one does not exist on the layer field.
