T-mobile iPhone 5 not receiving group messages?

I have an iPhone 5 on T-mobile service. I have an issue with receiving group messages in a group of 8 people including myself. I'm the only one who has T-mobile service, 5 of them have Verizon and the other 2 people have Sprint. I have had this phone for over a year and have never had an issue with receiving group messages with the same exact people. This all happened about 3 days ago and has been an issue ever since. I'm able to send out messages in the group but will not receive any of their messages until hours later or sometimes not at all. Individual messages come in just fine but group messaging will always be delayed. I've done everything I can think of to fix the issue. I've signed in and out of my Apple ID, turned MMS and Group Messaging on and off multiple times, swapped the SIM card in the phone twice (the last time was yesterday), reset all network settings, even erased the entire phone and restored from my iCloud backup. I'm not sure what else to do to fix the issue other than replace the phone. But if it's a network issue with T-Mobile then I'd rather not get a new phone. Anyone else experiencing this issue as well? If so are there any fixes for it?

Yes! I have this same issue! I have a group message with 3 people. I'm the only T Mobile but there are 2 other iPhones and 1 Android. I've been in this group for over 2 years with no problem but now a couple of months ago I started having issues. Sometimes the messages will come in all at the same time hours later but most of the time I don't get any. I went to the TMobile store yesterday, they did a network settings reset and then an All settings reset. They tried to tell me that I should turn off iMessage but that didn't make sense because I text other iPhones as well. Any other recommendations that people have would be GREATLY appreciated because I'm quickly losing my patience.