My screen shows spreadsheet with 45 rows.
When there is row 1 shown and I move cursor to any row of 1..45 and choose '/view/freeze cells/freeze first row' from the menu the first row is freezed which is OK.
When I move cursor to row 46 (so the screen shows rows 2..46) and choose '/view/freeze cells/freeze first row' nothing is freezed which is not OK.
This behaviour is not related to any spreadsheet content (works this way on new spreadsheet too).
This bug seems to be unrelated to cursor position. It's sufficient to leave cursor on row 1 and scroll the spreadsheet down few pages and select 'freeze first row' to show this error too.
Also having cursor on row 100 and showing rows 1..45 on the screen just works fine - the first row is freezed.
same behaviour in latest 220.127.116.11 release
same behaviour in latest 18.104.22.168.alpha1 build 6a03
Thanks for reporting this issue.
Dupe of bug 100666
*** This bug has been marked as a duplicate of bug 100666 ***