Did you test it in this order?
Or other way around? It would make sense then. The command/button Shows information about application updates shows cached information. While the command Check for updates does not. So if you first used the Shows ... command, it might have shown old data, while the Check for updates showed up to date data.

Anyway this was changed already for upcoming 5.6:
https://winscp.net/eng/docs/history_old#5.6

Toolbar button always checks for updates, instead of showing cached data, when available.

Hello,

I noticed this bug in the past and now it happened again:
You can check for new versions in 2 ways:
1. Clicking the button on the button bar at the right side ("Shows information about application updates")
2. From Help -> Check for updates.

However, the behavior is not consistent.

I just opened WinSCP and clicked the button. I got a message saying "You have the latest version".
Then I went to Help-> Check for updates and this time I was informed that "New version 5.5.2 was released"

Please see attachment with screenshots.

Regards,
M.R.