This issue has been present for almost 10 years now. Google has managed to identify the issue and it is specifically Verizon who won't publish the repair. I purchased a third party texting app who was willing to provide legit troubleshooting. Essentially what happens with Verizon and Android phones is there is the ability for text messages to have a collision effect. When this collision occurs all texting stops temporarily. I just had it happen not 10 minutes ago. It took upwards of 20mins for the collision to clear and my texts to go out and new ones come in. Its strictly about timing. The ONLY time this will happen is if you time it just right where the inbound text and the outbound text collide and get stuck. Android gets stuck trying to process the order in which things should occur and locks up.
One method that used to fix it was put your phone in airplane mode, wait for the failure to send message to appear then take your phone off airplane mode. All inbound texts would then load, then you could send your outbound texts. This makes group texting almost impossible on my device. But as of lately, this fix no longer works. So you need to patiently sit and wait until the text errors out, let the new inbound ones process, then send your text.
The issue can be replicated in Google Messages, Textra, Message+, QkSMS
