Error 500 only in quiz pages

Good moorning,

We’ve used Quiz and survey master plugin for the last year without problems in three different domains, and we are very satisfied; but recently we detected that in the last 15 days the pages that have the survey shortcode doesn’t work at all, in fact they give an HTTP ERROR 500. The other pages works correctly.

The references domains are:
https://www.institutocastelao.com/
https://comodejarelalcohol.es/
https://comodejarlacocaina.info/

examples of urls with survey shortcode and error 500:
https://www.institutocastelao.com/test-alcoholismo/
https://www.institutocastelao.com/test-cocaina/
https://comodejarelalcohol.es/test-alcoholismo/
https://comodejarlacocaina.info/test-cocaina/

We will apreciate your help to solve this problem, thank you in advance.