Same project and two Pcs

[caiov1n1c1us]

Three monitors. Two ultrawide and one 4k.
My dad uses only one 4k.

Could be that? Because I place all Lazarus windows between all 3 monitors.

Yes. Depending on which monitor you design the form there will be negative or very large positive Left values. Since the DockedFormEditor has an issue with negative Left values as reported by n7800 it will exactly produce the issue that you describe.

Gotcha! Glad to know.
Hope this topic help others in the future.

Thanks guys