Buck-Boost converter not working right when fed by dynamo
The bicycle "dynamo" you have shown in the schematic is an alternator. (A dynamo is an electrical generator that creates direct current using a commutator.) This means that the voltage on the input to your buck-boost converter will be seeing half-wave rectified AC unless the capacitor is big enough to maintain voltage during the valleys. (Why is there no C value shown on the schematic?)

If you edit your question to show an accurate schematic of your setup we may be able to help further.