The caffeine's finally kicked in, and I realised I could just ask Chrome to show me what both sites were doing differently...

In T6815#99704, @epriestley wrote:

If it's not too hard, it would likely be helpful.

I get the dialog on this installation. However, try as I might, I can't get it to pop up on ours. Same browser, settings, etc. Would a capture of the HTTP traffic on my install help to narrow down whether the problem is in the PHP code not reporting the error correctly, or the client-side JS not handling it correctly?

I'm sorry, I don't sign CLAs.

I dug in, and the attached diff is what I came up with. The problem was that by left joining with the IN ('open','inprogress') condition, you're not excluding any rows from the result set, you're just leaving all the values NULL. It's the WHERE that has to be modified, so that the rows don't get end up in the result set. I could have modified the join (to not filter on status) and then change the WHERE to check status IN ('open','inprogress'), but this seemed like the least invasive change.

Things are definitely looking better! I'm getting some of my all-closed-blocking-tasks tasks in my "Show Tasks Not Blocked By Other Tasks" search results. However, at least one task that I think should be found isn't being found (it's being shown in the "Show Tasks Blocked By Other Tasks" search, instead) even though all of the blocking tasks look done. Since I've got no idea what the difference is yet, I don't have a reproduction case for you. I'm going to dig into the query and debug what's going wrong. I'll let you know what I find.

I'm still getting the blank, greyed-over screen, running on d866af3. The exception message is improved, but it's still only showing up in the logs:

Just upgraded to e5e3eb3 and the problem still persists. Same UI, and the log message looks much the same to me:

Running on 18340d9 here; I'll be upgrading in the next couple of hours to master to fix T7421 if you'd like a retest. Looking at T6692, though, it looks like that was fixed back in Jan.

@chad, yes, I've just confirmed that the maniphest "Advanced Search" form also behaves in the same manner.

Oh balls. All that care and attention to get the description right, and then I go and make a n00b mistake. Thanks for the catch, @hach-que.