After an update from 1.5 to Joomla! 3.4.6 I have problems with the database of K2. Regularly chrasht _K2items the table with the following error:

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Table './geloofen/j25_k2_items' is marked as crashed and should be repaired SQL=SELECT i.*, c.name AS categoryname,c.id AS categoryid, c.alias AS categoryalias, c.params AS categoryparams FROM j25_k2_items as i LEFT JOIN j25_k2_categories c ON c.id = i.catid WHERE i.published = 1 AND i.access IN(1,1) AND i.trash = 0 AND c.published = 1 AND c.access IN(1,1) AND c.trash = 0 AND ( i.publish_up = '0000-00-00 00:00:00' OR i.publish_up <= '2015-12-18 11:26:28' ) AND ( i.publish_down = '0000-00-00 00:00:00' OR i.publish_down >= '2015-12-18 11:26:28' ) AND i.id=671
It appears that the page you were looking for does not exist.

The website does it again after I fixed the table, but this is not the intention that the website is still out.
What can I do?

Is there a spike in your traffic?
Since x__k2_items is generally the most used database table it is the one that would crash if there is a spike on your traffic, or the server's traffic.