The vast majority of 1:400 scale models have shown absolutely no signs of deterioration since they were built but there have been a small percentage of them, which have been impacted by various rots, bubbles and cracking. The most serious of these has been that of Zinc Rot, a phenomenon especially linked to one particular period in 1:400 history but also found in a few other places too. That doesn't mean that just because your model has some bubbles it has Zinc rot but nonetheless for certain models the risk of self-destruction is high.
What is Zinc Rot?
Zinc Rot is a well-known and understood process whereby the zinc used to make die-cast models deteriorates over time due to intercrystalline corrosion caused by lead impurities within it. The impact of Zinc rot is irreversible and is not affected by the manner of model display or storage. The damage can be variable across models and even units of the same release. So, it is entirely possible that of two examples of the same model one is fine while the other rots. Likewise depending on the levels of impurities within the Zinc some models are worse affected than others.
At its worst huge cracks appear across the model, wings bend upwards and snap and the model eventually falls apart. It may start as small cracks, blisters or pitting but if it is zinc rot then it will steadily get worse.
It may also only impact specific parts of a model i.e. engines and undercarriage. I have had several examples where one or both of the main undercarriage legs on SMA and Aeroclassics 737-200s has rotted but the rest of the model is fine. There have also been examples of Aeroclassics 707s where only an engine has rotted.
Some brands are notorious for bubbling (Magic Models for example) but bubbling is not necessarily the same as zinc rot and may be caused by other production failings. A model with bubbling will not necessarily develop Zinc rot symptoms. Likewise there are other types of rot out there such as powdery rot which impact models, many of which aren't made of Zinc at all - see here for more on this.
When has Zinc Rot Occurred?
There are examples of cracking and 'rot' in models dating throughout the history of 1:400 scale but it has only been seen on a large scale once. This became apparent in 2007 when models made during 2002 and 2003 at the Jinbo factory began to show signs of the rot. The Jinbo factory that was responsible at the time for the production of Aeroclassics, Big Bird and Seattle Models Co, so it is these three brands that have been primarily associated with the problem. The discover of the problem was a major reason for Aeroclassics leaving the Jinbo factory in 2007.
It is highly likely that the vast majority, if not all, of models from the 2002-2004 period have already rotted so if you have surviving models from that time period they are likely to be fine. There have been no reports of any Aeroclassics or Big Bird models being impacted from outside this relatively short period.
More recently several Gemini Jets releases have also shown susceptibility to serious rot issues. The Portland Timbers 737 is notorious. Quite why only specific models across multiple years seem to be impacted is hard to say.
What Models Are Impacted?
The below is a no doubt incomplete list of impacted models by manufacturer. Starting with the Jinbo factory problem from 2002-2004:
Here are other models reported to be impacted by Zinc rot. It is possible that some do not have true zinc rot:
Lastly these are more recent Gemini releases impacted by Zinc Rot: