a single page 404 error

[Ampersand]

After importing pages from an old 2.03 version to current 3.3.8, I started to receive 404 on one of the pages.
I saw 404 page from normal links leading to this page and from edit.php after pressing preview.
I tried checking private in page options. No change.

I removed all content from the page - still the same.
I copied page content to another new page with a different url. Page displayed normally.

Still diagnosing it , but may be I made some mistake on import resulting in such behavior?

Update:
mysite.com/xv-sesja-rady-miasta-8-lutego-2016 => GS 404 page
mysite.com/index.php?id=xv-sesja-rady-miasta-8-lutego-2016 => page looks fine

[Ampersand]

Well looks like a fake alarm. Page displays fine on a mobile phone using a different internet provider. On my desktop still 404. Looks like my browser cache or Internet Service Provider cache. Annoying.