CCP today released a developer update on ESI reminding people that the XML API and CREST will be turned off on May 8.  This means that all third-party tools which have not yet switched over to ESI will need to do so in the next 30 days before they cease to function.

CCP Explorer also made a series of tweets regarding the changes in which he said that there will likely be no resolution to ongoing issues with XML API. He also expressed concern about the number of apps which are still using CREST:

Looking at the CPU usage of the CREST nodes then I'm slightly surprised and even somewhat concerned about the still relatively high usage.

— CCP Explorer (@CCP_Explorer) April 9, 2018

If you are a third party developer who has not yet made the change, now is the time to begin switching over.  If you are a user who imports CREST or XML API into your spreadsheets, now is a good time to look into using ESI with them. CCP have documentation on how to integrate with google sheets on their third-party devblog.