For what it is worth, when I used to use Emsisoft Anti-Malware as my primary security software in real-time back in 2014/2015, updating the signatures/product would always cause a short freeze/slow-down but only for a few seconds. It was only a few seconds and would have only happened if the GUI was opened at the same time therefore I never really saw it as a "problem". I've experienced a lot of this with many other security software products as well over the years.
You could let Emsisoft know and they could see if they can diagnose why this is happening but I wouldn't worry about it unless its really causing a problem for you, after all you did mention it was only around 4 seconds for you as well. Maybe they already know about the issue and just cannot fix it yet for some reason, I am not sure.