Great that it's back to normal. Sluggish performance not so great.
Could be a number of reasons for that. We are aware that calendar gets slow if there are thousands of events, and if it's an event being synced to a server it will add time and potential causes for delay. Other things in the browser can also affect this, there have f.ex. been some cases of mail acting up recently which can cause considerable load. Would be good to hear back if this is a persistent problem. And also do continue to report any issues you have with the templates.