Quiz

You are right the problem is in the eval function line 930 of the question/type/formulas/variables.php file.

According to a comment on the page http://php.net/manual/fr/function.eval.php this function has changed in php 7.x from just returning false to terminating the script if the evaluated code generate a fatal error

Most probably the solution is to include it in a try {  } catch block

Unfortunately I will not be able to commit the change after having fully tested it (and release a new version until Friday (sorry Family constraints !)

Maybe if you are brave enough you can test to replace this line with something like

            try {
                eval('$res = '.implode(' ',$splitted).';');
            } catch (Throwable $t) {
                throw new Exception(get_string('error_eval_numerical','qtype_formulas'));
            }