I was on a BRU-AMS-LHR mid-afternoon itinerary last week when the E190 operating the AMS-BRU-AMS flight apparently went tech and returned to the Fokker Farm at AMS (caught its runway movement live). Started to look at reaccommodation as we'd miss the LHR connection (only 1:10) once I got the notification that we'd miss the connection. All the KL (and AF) app was only offering was itineraries the next day. I would have been tempted to take ta flight the next day and have an extra day in Brussels with hotel and meals and EU261 comp at KL's expense if I didn't have things to do with a tight schedule in London. As it was, I called KL and they couldn't do anything until the connection was definitely missed. Did call the PSL while waiting to board the delayed flight (another E190 was rustled up) who put me on the next LHR flight (delay was only 2 hrs).

Likely low availability on that flight and the automatic rebooking mechanism keeping a few seats free. The PSL can likely override that, and as you have status, put you on that flight anyway. Which may be the exact reason why they don't automatically rebook that flight up to 100% straight away.

In my experience of irrops on KLM, they can be very slow at proposing automatic alternatives, and they usually propose a next-day solution before closer-in options are proposed.

Of course, it this occurs late in the day, it's likely that you won't get a second wave of options proposed.

In any case, you should not simply accept whatever the app tells you - if you're at their hub airport go to an agent, or else ring up.

Even without any status at all, they would rebook you on that flight rather than having your overnight somewhere. The automatic algorithms are quite imperfect but the humans will always give you anything even remotely reasonable.

The later AMS-LHR flight had lots of room (I don't think it was more than 1/2 full, as was the delayed BRU-AMS flight). Definitely not an availability issue.

Gave me time to visit the non-Schengen lounge for the first time in 13 years.