Lookup fields with autocomplete are not reliably loading a list of matching records

We are seeing some intermittent performance issues, particularly around lookup fields.

As an example, on our main Contact override page, we load in several related models, particularly Affiliations and Relationships (we use NPSP on Salesforce). When we want to add a new Relationship to a Contact - we have an autocomplete lookup field in a table where the user is supposed to type the name of the person they want to create a connection for. The issue is that sometimes this works exactly as designed - they start typing and quickly see a list of all matching Contacts. However, sometimes the loading circle will spin on the right hand side of the lookup field for a seemingly infinite amount of time. It seems that it is somehow getting hung up in its search. If you delete a few letters and retype them a few times, sometimes that will make the search results appear. Sometimes you have to delete and retype the whole name except for the last letter. Sometimes you have to reload the whole page. 

The same behavior will occur sometimes on other autocomplete fields connected to other models, so I don’t think its necessarily related to Contacts specifically. I can try to keep an eye out for which ones in particular seem to be problematic if that is helpful. Is anyone else experiencing anything like this?