The pre tag is a security measure to avoid malicious / unintended html constructs and possible php escapes.
Somewhere the nowrap has been set and needs to be removed out of the css classes "reminder_overdue, reminder_due, reminder" that is in $extra or some inheritance.
Hope you have installed the dashboard theme and edited the default.css there by removing the erroneous last "*/" as per this commit.
There are several instances of white-space: nowrap; in the dashboard theme's default css file (as in all other themes) that may have got inherited suffers defaults.
https://www.w3schools.com/cssref/css3_pr_word-wrap.asp
https://www.w3schools.com/cssref/css3_pr_flex-wrap.asp
https://www.w3schools.com/cssref/css3_pr_text-wrap.asp
https://stackoverflow.com/questions/3949762/how-to-wrap-text-using-css
http://www.xanthir.com/b4U10
The better option if you cannot control user input, it is to establish the css property, overflow:hidden, so if the string is superior to the width, it will not deform the design.
The following should work everywhere:
<div style="word-wrap: break-word; width: 100px"> gdfggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggggg</div>