Failed to open /proc/self/stat

I have some code that periodically reads /proc/self/stat on centos 7.

The code is written in C++.

This has been running fine for over a year but today on dozens of servers in many different time zones at the same time my code was not able to open /proc/self/stat.

My code did not handle failure to open /proc/self/stat which is obviously something I should fix but I really would like to understand how it is possible that /proc/self/stat is not available and how this can happen to all servers at the same time.

Would greatly appreciate your insights.