Pack only has 5 cards
 

is this a bug?

This just a display error, likely the card title was not properly downloaded. You still got the card and you can find it in your cards list, although it will be hard to tell which one it was I imagine.

Standard Pack @ 24. Mar 2019 07:08:07 UTC:
MLB 2019 Live, RP Anthony Banda, TB, 2019 - in use
MLB 2019 Live, CF Leury Garcia, CWS, 2019 - in use
MLB 2019 Live, 3B Rio Ruiz, BAL, 2019 - quicksold
MLB 2019 Live, SS Blake Trahan, CIN, 2019 - quicksold
MLB 2019 Live, SP Dan Straily, MIA, 2019 - quicksold
Unsung Heroes, SP Micah Owings, ARI, 2008 - in use

The "Micah Owings" card was generated but somehow lost during the transmission to the client.

I've seen this too.

It seems like you don't get the card because I see only 5 new players on my reserve roster.

Unless the card is going to the inactive list, which as you said could be very hard to find. :unsure: