site goes down form no apparent reason

Hello,
once in a few weeks my site goes down for no apparent reason (it just ?happened).

I talked with my hosting company but they couldn’t find the ?problem.

The weird thing is that the sitemap.xml does work! ?

This is the site: https://www.productivewise.com
And this is the sitemap.xml: https://www.productivewise.com/sitemap.xml ?

Does anybody have an idea what may cause it??

thanks!
Eyal.