Usually the cause is inexplicable because some things just don't work correctly even when calling all commands by their full path.
Usually adding the following to your crontab file at the top will fix/solve the issue:
A VPS Server I had just wasn't working right, code that I migrated there just wasn't working. For example, it kept telling me the connection to the database was unsuccessful, halfway through iterating through results it already had.
Then I realized it wasn't my code. Ichecked my /proc/user_beancounters and found this:
uid resource held maxheld barrier limit failcnt........