When using a struct with more than 32 variables, the struct window will not display them all, nor is there a vertical scroll bar. Also the right section to add or modify a new or existing variable is not displayed.
In the screenshot, I have 33 variables currently (Superconductivity is below the ElectricalResistivity variable)
After doing a bit of digging I found that this is a known issue. I have provide a link to the public tracker. Please feel free to use the link provided for future updates. I hope that this information helps.