I played Sweden to check if a minor with tank designs could actually build them, and by the time I got to the 1939 tank, the production window breaks, where all the buttons are shoved up so high you cannot click on them, and you cannot scroll the tab.

On top of this, possibly due to me not owning the DLC that gives the tank designer, researching a tank only gives the hull, and I have no option to actually get tanks out of the research. There also are no presets in the production tab for anything but the starter tank.

Ran into the same issue with tanks as Hungary, when by 1940 when I started to think about tank stuff and had researched some, the tab broke and I couldn't see the tech, nor could I build any due to the "Design lacks one or more required modules" notification on the hull.