Can't enter backend after editing pages on Sitemap

I am having trouble developing Concrete5 Website.
I was editing pages on Sitemap menu like moving pages, making external links changing orders of the pages.
After that, I found I cannot enter the dashboard of Concrete5.

Website is still showing normally, Concrete5 admin bar as well.
However, when I click the hamburger menu, the menus appear normally, but even though I click any menu like Sitemap, Files, Members - all redirect to the homepage.

I have one screen showing sitemap that I opened before editing the sitemap, and it shows Load error when I try to open 2nd level.
In debugging tool, I can see the error like this:
fancytree.js:1 <FancytreeNode(#162, 'Services')> Load children failed ()

I reckon some page consistency is broken but I don't know how to fix it.
Has anyone experienced this situation?

Concrete5 Ver 8.1.0

View Replies:
ob7dev replied on at Permalink Reply
I would try upgrading the c5 version by uploading the newest version to your updates folder then updating from the admin panel. 8.1 was a bit buggy and updating could solve the problem. If an update doesn't fix it then something might have gone wrong with the database.
NMasa replied on at Permalink Reply
Hi ob7dev,

Thank you for advice.
I don't have enough time to investigate, so I recreated from the beginning (css file, template files are no problem and luckily, it's not a huge website).
I'll try updating Concrete5, it might solve the consistency of database.