Update: KLM has provided some additional details and clarifies their policy (a little).
They are now saying the ban on checked bag transfers only applies to flights that originate in Europe, connect in AMS, and continue on to another European airport.
Here's what's now posted on their website:
Operational issues at Amsterdam Airport Schiphol
We’re currently facing operational issues for flights departing from Amsterdam Airport Schiphol, leading to long waiting times at the airport. Here’s our up-to-date overview with more information and tips on what you can do.
If you travel from another airport, please note that during this summer, many are facing similar challenges. Please find information about local constraints and waiting times on the airport's website of your departure.
Schiphol’s baggage system malfunction
What is the result of the malfunction?
On Wednesday, 20 July, Schiphol’s baggage system malfunctioned. As a result of this disruption, KLM could not process baggage during a significant part of the day. Unfortunately, thousands of suitcases of our passengers were left behind in Amsterdam.
Is the baggage system working again?
Yes, the baggage system is working. However, measures are still in place and might affect your flight on Thursday 21 July.
What preventive measures has KLM taken?
To prevent passengers from being harmed further, measures are in place on Thursday 21 July. Passengers departing from a European destination and flying to another European destination – with a transfer in Amsterdam – can only take hand baggage with them. Alternatively, passengers can rebook their flight.
This measure does not apply to passengers departing from the Netherlands and does also not apply to passengers whose final destination is Amsterdam.
Taking this measure gives us room to send as many suitcases as possible that were left behind on Wednesday.
Can I rebook my flight or request a travel voucher?
f you are not able to travel with hand luggage only, you can choose to rebook your flight free of charge or request a travel voucher yourself in just a few steps. To view your options, simply log in to My Trip on KLM.com using your booking code and last name.
Rebook flight (link)
Request a travel voucher<link>
Other notes:
It's not entirely clear if this limitation is only for KLM (which admittedly is the largest operator in AMS) or if it's impacting other airlines, too. The messaging is all coming from KLM (I've seen not a single word about this from other airlines), so it appears other carriers may not be doing this.
I'm reading elsewhere that KLM has not been consistent in their rebooking policy. Some reports of people saying they can't manage with carry-on only have requested to rebook on another date, but have been told they have to pay the standard (expensive) "change fee" to rebook on another date when checked baggage will be allowed; some others have said they were rebooked with no additional charge and no fuss. Not exactly KLM's finest hour.
They still have not clearly defined what constitutes "Europe" for the purposes of this exercise (the EU? Schengen? the Holy Roman Empire?) but that will soon be moot.
The good news is that the sun will be setting shortly in Amsterdam, and in a few hours this no-checked-bags policy should just be part of our memories of the Summer of Travel Challenges (until the next thing happens).
Hug your kids. And your suitcases.