As Doug Chasman answered on this question [this link][1] there is an issue with static resources in Spring'17. The issue is being tracked in R&D by W-3615844

Except this, are you that you're targeting the div correctly when calling Highcharts ? Maybe try with a component.find or document.getElementById ?

  [1]: http://salesforce.stackexchange.com/questions/155236/lightning-component-scripts-loading-issues-since-spring-17-update/155264#155264