Prebiotic gas is not random. It often comes from fermentation.
When gut bacteria use certain fibres, gas can be produced along with other compounds. This is normal biology, but it can feel uncomfortable if the change is sudden. Inulin, FOS, GOS, legumes, onion, garlic and some fruits can all be more noticeable for sensitive people.
Other fibres may feel gentler because they ferment more slowly, are used in smaller doses, or create less rapid gas for that person. PHGG and acacia fibre are often chosen for daily gut health products for this reason. Psyllium husk is different again, because its main behaviour is gel formation and water holding rather than heavy fermentation.
The practical lesson is to stop judging fibre only as good or bad. Ask how it behaves. Does it thicken? Does it ferment quickly? Does it need more water? Does it suit your current diet?
If prebiotics cause gas, reduce the dose rather than quitting immediately. Take them with meals. Increase slowly. Avoid adding multiple new fibres together. Cook beans well and start with smaller portions.
The microbiome likes fibre, but the gut likes patience. Gentle progress usually beats aggressive dosing.
Do not sort fibres into good and bad. Sort them by how fast they ferment, then dose accordingly.