why does the samsung phone drop off once two iphones are texting

This involves 3 phones. Two are iphones. one used to be and is now a droid. The droid # has been deleted and re-entered in contacts when it went from the iphone to the droid. When an iphone texts the droid and the 2nd iphone, everyone gets the msg when the 2nd iphone texts back the droid no longer gets the messages.The messages started off green and then go blue once the 2nd iphone texts.

The droid has deactivated the # with Apple iphone. Both iphones have iMessage; send as SMS, MMS messaging and Group messaging on.

Does anyone have any ideas why the droid drops?