Freezing rows makes buttons disappear

Freezing rows makes buttons disappear

Dear Zoho Team

Please refer to the following link:
https://docs.zoho.com/sheet/published.do?rid=hd3vb8ba293ada0d94daead4e79f9868039f8

At the top of the page I have created selection buttons A - Z. I want to freeze rows 1 - 4, but as soon as I do this all buttons disappear. If I unfreeze rows 1 - 4, the buttons are back again. 

Can you please help me? Thank you very much.

Kind regards
Hans