We had the incident where when you executed the following command (pwdlist.txt has exactly 1 password, users file has 5 users):
/o365spray.py --spray -U ../users.txt -P ../pwdlist.txt --domain somedomain.com
that it would stop/crash after finding the first valid user credential, followed by an invalid one.
As long as the following users all had valid credentials it kept running.
We tested the EXACT same command again later with no problems. Looks like something funky is going on here