This happened to me on a Samsung Galaxy S8Plus (running Pie) yesterday, after having installed a recent security update on Friday. I tried making calls but they never connected, or so I thought when I abandoned the calls. What happened this morning is that I tried dialing *611 to get tech support, but seemingly it failed so I put the phone down. Apparently the call did connect without my knowing it and VZW support got the call, the CSR listened to background noise and decided to call me back to see if something was wrong or if it was a buttdial.
So, I spent nearly two hours with VZW tech support walking through comprehensive troubleshooting. Finally, tech support issued me a new SIM card which I could pick up at a local retailer. An hour after the new SIM was installed, the post dial delay has disappeared, outbound calls now connecting in 2-3 seconds again. Definitely something with VZW but they said nothing about problems in the network. Sigh. At least I didn't have to do a reflash of the whole phone.