Welcome @TomasWayTo, to the community!
Your problem probably has to do with your layout: you have routed the track for feedback directly under the coil L1, so that the track captures the magnetic switching signals from L1 and thus interferes with U1. As the input voltage increases, the duty cycle becomes smaller and smaller (the switching pulse becomes shorter and shorter), which has an influence on the control as a higher-frequency interference.
As a workaround, you can disconnect pin 9 (FB) from the track and replace the connection with a wire that runs around L1 in a wide arc.
Regards
/Peter
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