I recently upgraded from 10.3 to 10.4 and I started having issues with some forms with lookupstarted and onloadlookupfinished after the upgrade. 

The form starts a CSS loader (which works fine):

$(document).on('lookupstarted', function(event) {
        console.log("onloadlookupstarted event");
        $('#loader, .loader').show();
    });

and it turns off when there's a lookup finished (which works fine when it's called): 

$(document).on("onloadlookupfinished",function (event) {
        console.log("onloadlookupfinished event");        
        $('#loader, .loader').hide();

}

Since the upgrade, a 'lookupstarted' event doesn't seem to be 1:1 with an onloadlookupfinished. I'm not sure if it's something I'm doing wrong with my lookup rules, javascript, or a bug in 10.4. Wondering if anybody else is having this issue or has any insight.

It seems that if I only run a single lookup rule I get consistent onloadlookupfinished events:

with three lookups:

 ...however, once I start enabling a few more rules (there are 23 lookup rules total) I get a lot of lookupstarted events and no onloadlookupfinished events after the first event:

When I enable all 23 rules, a lot of onloadlookupstarted events and no finished events: