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Why does my CNN suddenly start giving NaN loss after a few training steps?
This happens because invalid numerical values are entering the network, usually from broken data or unstable gradients. In CNN pipelines, a single corrupted image, division by zero during normalization, or an aggressive learning rate can inject inf or NaN values into the forward pass. Once that happRead more
This happens because invalid numerical values are entering the network, usually from broken data or unstable gradients.
In CNN pipelines, a single corrupted image, division by zero during normalization, or an aggressive learning rate can inject
inforNaNvalues into the forward pass. Once that happens, every layer after it propagates the corruption and the loss becomes undefined.Start by checking whether any batch contains bad values:
if torch.isnan(images).any() or torch.isinf(images).any():
print("Invalid batch detected")
Make sure images are converted to floats and normalized only once, for example by dividing by 255 or using mean–std normalization. If the data is clean, reduce the learning rate and apply gradient clipping:
torch.nn.utils.clip_grad_norm_(model.parameters(), 1.0)
Mixed-precision training can also cause this, so disable AMP temporarily if you are using it.
See lessWhy does my vision model fail when lighting conditions change?
This happens because your model has learned lighting patterns instead of object features. Neural networks learn whatever statistical signals are most consistent in the training data, and if most images were taken under similar lighting, the network uses brightness and color as shortcuts. When lightiRead more
This happens because your model has learned lighting patterns instead of object features. Neural networks learn whatever statistical signals are most consistent in the training data, and if most images were taken under similar lighting, the network uses brightness and color as shortcuts.
When lighting changes, those shortcuts no longer hold, so the learned representations stop matching what the model expects. This causes predictions to collapse even though the objects themselves have not changed. The network is not failing — it is simply seeing a distribution shift.
The solution is to use aggressive data augmentation, such as brightness, contrast, and color jitter, so the model learns features that are invariant to lighting. This forces the CNN to focus on shapes, edges, and textures instead of raw pixel intensity.
See lessWhy does my autoencoder reconstruct training images well but fails on new ones?
This happens because the autoencoder has overfit the training distribution. Instead of learning general representations, it memorized pixel-level details of the training images, which do not generalize. Autoencoders with too much capacity can easily become identity mappings, especially when trainedRead more
This happens because the autoencoder has overfit the training distribution. Instead of learning general representations, it memorized pixel-level details of the training images, which do not generalize.
Autoencoders with too much capacity can easily become identity mappings, especially when trained on small or uniform datasets. In this case, low loss simply means the network copied what it saw.
Reducing model size, adding noise, or using variational autoencoders forces the model to learn meaningful latent representations instead of memorization.
Common mistakes:
Using too large a bottleneck
No noise or regularization
Training on limited data
The practical takeaway is that low reconstruction loss does not mean useful representations.
See lessWhy does my object detection model miss small objects even though it detects large ones accurately?
This happens because most detection architectures naturally favor large objects due to how feature maps are constructed. In convolutional networks, deeper layers capture high-level features but at the cost of spatial resolution. Small objects can disappear in these layers, making them difficult forRead more
This happens because most detection architectures naturally favor large objects due to how feature maps are constructed. In convolutional networks, deeper layers capture high-level features but at the cost of spatial resolution. Small objects can disappear in these layers, making them difficult for the detector to recognize.
If your model uses only high-level feature maps for detection, the network simply does not see enough detail to identify small items. This is why modern detectors use feature pyramids or multi-scale feature maps. Without these, the network cannot learn reliable representations for objects that occupy only a few pixels.
Using architectures with feature pyramid networks (FPN), increasing input resolution, and adding more small-object examples to the training set all improve this behavior. You should also check anchor sizes and ensure they match the scale of objects in your dataset.
See lessWhy does my medical imaging model perform well on one hospital’s data but poorly on another’s?
This happens because the model learned scanner-specific patterns instead of disease features. Differences in equipment, resolution, contrast, and noise create hidden signatures that neural networks can easily latch onto. When the model sees data from a new hospital, those hidden cues disappear, so tRead more
This happens because the model learned scanner-specific patterns instead of disease features. Differences in equipment, resolution, contrast, and noise create hidden signatures that neural networks can easily latch onto.
When the model sees data from a new hospital, those hidden cues disappear, so the learned representations no longer match. This is a classic case of domain shift.
Training on multi-source data, using domain-invariant features, and applying normalization across imaging styles improves cross-hospital generalization.
Common mistakes:
Training on a single source
Ignoring domain variation
No normalization between datasets
The practical takeaway is that medical models must be trained across domains to generalize safely.
See lessWhy does my reinforcement learning agent behave unpredictably in real environments?
This happens because simulations never perfectly match reality. The model learns simulation-specific dynamics that do not transfer. This is known as the sim-to-real gap. Even tiny differences in friction, timing, or noise can break learned policies. Domain randomization and real-world fine-tuning heRead more
This happens because simulations never perfectly match reality. The model learns simulation-specific dynamics that do not transfer.
This is known as the sim-to-real gap. Even tiny differences in friction, timing, or noise can break learned policies.
Domain randomization and real-world fine-tuning help close this gap.
Common mistakes:
Overfitting to simulation
No noise injection
No real-world adaptation
The practical takeaway is that real environments require real data.
See less