Generally, this Xero error code 500 triggers when users have open so many operations on the screen or use some special characters in the text fields and some massive records.
with the help of this Presentation, you will able to clear cookies from various Browsers and improve xero's Functionality. Source: https://xeosupportaustralia.wixsite.com/xerosupportnumber/single-post/Clear-Cookies-to-Improve-Xeros-Functionality