I haven't gathered enough data on this to figure it out, so maybe it's Yet Another Feature I'm Still Learning About Stack Exchange.
I have several queries in SEDE; my typical SEDE usage is:
- load the U&L SEDE page
- click Log In
- Select the authentication method
- (successfully log in)
- Click on my profile link
- Click on the "favorite" tab
At that point, when I click on one of queries, it loads the query, but then sometimes goes ahead and automatically executes it, as if I had clicked "Run Query". Other times, it simply loads the query. I noticed that when SEDE runs a query, I get a stacking timer of sorts in the upper left corner. When SEDE simply loads the query but does not run it, I get a single timer in the upper left.
This is not a situation where I'm trying to run more than two queries at a time.
I am logged in to SEDE at the time -- no captcha prompts involved.
My random guesses:
- random chance
- length of query
- current system load
- my immediate history / interaction with SEDE
- phase of the moon