Thanks for your report.
I have sent you an email with a debug version of WinSCP to address you have used to register on this forum.

<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>

searched for text within an opened file. pressed F3 to 'search next'. Window lost focus (was pushed to the bottom of the stack). when I clicked on the document INSTEAD of the 'ok' from the 'no more matches' window, WinSCP crashed.

<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 5.7

Error message:
Invalid access to memory.

Stack trace:
[014369BB] Vcl::Forms::TCustomForm::IsFormSizeStored
[779FB466] ntdll.dll