Msmtp: sending two emails at once doesn't work?

Hello !
I installed msmtp in March and set a ping-monitor for my access points: if ping to the APs doesn't go through, I get an email (and another one when it's working again). I "wrote" a xxx.sh file (just modified the file I found on-line) and put it on cron for every minute. It's been working fine.

Now, I wanted to get an SMS for ping-failure of some of the APs (not all of them, just a few important ones) as well. Somebody offered me to use an Email-to-SMS service for free associated with a certain email, so I wrote another yyy.sh file and have a ping-failure message sent to that email address (then it sends an SMS).

Both .sh files work fine if I just execute them individually. I get EMail resp. SMS as I expect. But, cron execute them both at the same time, and as I restarted one of these important APs, I only got SMS, but not an email as I used to.

I am wondering if msmtp has difficulty with sending emails to two different addresses at the same time. It is using smtp.google.com.

I would appreciate if someone could please let me know if I'm doing something wrong, or what else is wrong....