Cannot change Visible in OnShow or OnHide

<Try to describe precise steps that lead to the problem (where do you click, what keys do you press, what do you see, etc.)>
<If relevant, consider attaching a session log file or a screenshot)>

WinSCP 5.10

Error message:
Cannot change Visible in OnShow or OnHide

Stack trace:
(00215B14)
(00834B88)
(00257A85)
(00211F4C)
(008385B4)

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.